:root {
            --primary: #18324b;
            --primary-hover: #10283e;
            --primary-light: #eaf1f5;
            --secondary: #147d78;
            --success: #18764d;
            --success-light: #eaf6ef;
            --danger: #bd3b36;
            --danger-light: #fff0ef;
            --neutral-dark: #203344;
            --neutral-muted: #607181;
            --neutral-light: #f5f7f8;
            --border-color: #dce4e8;
            --side-hypotenuse: #2563eb;
            --side-opposite: #15803d;
            --side-adjacent: #ea580c;
            --card-shadow: 0 12px 32px -18px rgba(24, 50, 75, 0.28);
            --radius: 18px;
        }

        * {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
        }

        body {
            font-family: system-ui, -apple-system, "Segoe UI", sans-serif;
            background-color: #f3f5f5;
            color: var(--neutral-dark);
            line-height: 1.5;
            min-height: 100vh;
            padding: 32px 20px;
        }

        .container {
            max-width: 1120px;
            margin: 0 auto;
        }

        /* Header Navigation */
        header {
            background: white;
            border-radius: var(--radius);
            padding: 18px 26px;
            margin-bottom: 22px;
            box-shadow: var(--card-shadow);
            display: flex;
            flex-direction: column;
            gap: 12px;
            align-items: stretch;
            border: 1px solid var(--border-color);
        }

        .site-header-main {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            justify-content: space-between;
            gap: 12px 20px;
        }

        .brand {
            display: flex;
            flex: 1 1 480px;
            min-width: min(100%, 280px);
            align-items: center;
            gap: 12px;
        }

        .brand-icon {
            display: block;
            width: 132px;
            height: 100px;
            flex-shrink: 0;
            object-fit: contain;
        }

        .brand-title {
            min-width: 0;
        }

        .brand-title .brand-name {
            font-size: 1.15rem;
            font-weight: 700;
            color: var(--neutral-dark);
        }

        .brand-title p {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            gap: 6px;
            margin-top: 3px;
            font-size: 0.8rem;
            color: var(--neutral-muted);
            line-height: 1.4;
        }

        #current-chapter-title,
        #header-meta {
            display: inline-flex;
            align-items: center;
            min-height: 24px;
            padding: 3px 8px;
            border: 1px solid var(--border-color);
            border-radius: 999px;
            background: var(--neutral-light);
        }

        #current-chapter-title {
            color: var(--primary);
            font-weight: 700;
        }

        #header-meta[hidden] {
            display: none;
        }

        #header-meta {
            display: inline-block;
            white-space: nowrap;
        }

        .site-header-actions {
            display: flex;
            flex: 0 0 auto;
            align-items: center;
            justify-content: flex-end;
            gap: 10px;
        }

        .header-stats {
            display: none;
            align-items: center;
        }

        .assessment-active .header-stats {
            display: flex;
        }

        .stat-badge {
            background: var(--neutral-light);
            border: 1px solid var(--border-color);
            padding: 6px 14px;
            border-radius: 20px;
            font-size: 0.85rem;
            font-weight: 600;
            display: flex;
            align-items: center;
            gap: 6px;
        }

        .header-home-link,
        .header-home-link:visited {
            display: inline-flex;
            align-items: center;
            justify-content: center;
            min-height: 38px;
        }

        .header-home-link[hidden] {
            display: none;
        }

        .header-home-link {
            padding: 9px 13px;
            border: 1px solid var(--border-color);
            border-radius: 9px;
            background: var(--neutral-light);
            color: var(--primary);
            font-size: 0.82rem;
            font-weight: 750;
            text-decoration: none;
            white-space: nowrap;
        }

        .header-home-link:hover,
        .header-home-link:focus-visible {
            border-color: var(--secondary);
            background: var(--primary-light);
        }

        .header-home-link:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 2px;
        }

        .site-footer {
            margin: 36px -20px -32px;
            padding: 38px 20px 18px;
            border-top: 1px solid #26384d;
            background: #0b1329;
            color: #cbd5e1;
            font-size: 0.82rem;
        }

        .site-footer-inner {
            max-width: 1120px;
            margin: 0 auto;
        }

        .site-footer-grid {
            display: grid;
            grid-template-columns: minmax(0, 2fr) repeat(2, minmax(150px, 1fr));
            gap: 28px;
            padding-bottom: 26px;
            border-bottom: 1px solid #263448;
        }

        .site-footer-brand {
            max-width: 460px;
        }

        .site-footer-brand strong {
            display: block;
            margin-bottom: 8px;
            color: white;
            font-size: 1.05rem;
        }

        .site-footer-brand p {
            color: #94a3b8;
            font-size: 0.82rem;
            line-height: 1.65;
        }

        .site-footer-section h2 {
            margin-bottom: 11px;
            color: white;
            font-size: 0.72rem;
            font-weight: 800;
            letter-spacing: 0.08em;
            text-transform: uppercase;
        }

        .site-footer-section ul {
            display: grid;
            gap: 8px;
            list-style: none;
        }

        .site-footer a {
            color: #cbd5e1;
            font-size: 0.8rem;
            text-decoration: none;
        }

        .site-footer a:hover,
        .site-footer a:focus-visible {
            color: white;
            text-decoration: underline;
        }

        .site-footer a:focus-visible {
            outline: 2px solid #84cc16;
            outline-offset: 3px;
        }

        .site-footer-bottom {
            display: flex;
            align-items: center;
            justify-content: space-between;
            gap: 10px 20px;
            padding-top: 16px;
            color: #94a3b8;
            font-size: 0.74rem;
        }

        .subject-portal {
            display: grid;
            grid-template-columns: 250px minmax(0, 1fr);
            min-height: min(760px, calc(100vh - 180px));
            overflow: hidden;
            border: 1px solid #26384d;
            border-radius: var(--radius);
            background: #081629;
            box-shadow: var(--card-shadow);
        }

        .subject-portal[hidden],
        .workspace-breadcrumb[hidden] {
            display: none;
        }

        .subject-sidebar {
            display: flex;
            flex-direction: column;
            padding: 18px 14px;
            border-right: 1px solid #243448;
            background: #071221;
        }

        .subject-sidebar-heading {
            padding: 4px 10px 12px;
            color: #78889a;
            font-size: 0.67rem;
            font-weight: 800;
            letter-spacing: 0.12em;
            text-transform: uppercase;
        }

        .subject-track-list {
            display: grid;
            gap: 5px;
        }

        .subject-track-button {
            display: flex;
            width: 100%;
            min-height: 45px;
            align-items: center;
            justify-content: space-between;
            gap: 8px;
            padding: 9px 10px;
            border: 1px solid transparent;
            border-radius: 9px;
            background: transparent;
            color: #c3ceda;
            font: inherit;
            font-size: 0.78rem;
            font-weight: 700;
            text-align: left;
            cursor: pointer;
        }

        .subject-track-button:hover {
            background: #101f32;
        }

        .subject-track-button[aria-current="true"] {
            border-color: #244e46;
            border-left: 3px solid #78c936;
            background: #10233a;
            color: white;
        }

        .subject-track-button:focus-visible,
        .subject-chapter-card:focus-visible {
            outline: 3px solid #d9b66f;
            outline-offset: 2px;
        }

        .subject-track-name {
            display: flex;
            align-items: center;
            gap: 9px;
        }

        .subject-track-glyph {
            display: inline-grid;
            width: 25px;
            height: 25px;
            flex: 0 0 auto;
            place-items: center;
            border: 1px solid #31445b;
            border-radius: 7px;
            color: #78c936;
            font-family: Georgia, "Times New Roman", serif;
            font-size: 1rem;
        }

        .subject-track-count {
            color: #8695a5;
            font-size: 0.65rem;
            white-space: nowrap;
        }

        .subject-sidebar-footer {
            margin-top: auto;
            padding: 16px 10px 2px;
            border-top: 1px solid #243448;
            color: #8491a0;
            font-size: 0.72rem;
        }

        .subject-sidebar-footer strong {
            display: block;
            margin-bottom: 3px;
            color: #e4e9ef;
        }

        .subject-catalog-content {
            min-width: 0;
            padding: clamp(22px, 4vw, 42px);
            background:
                radial-gradient(ellipse at 86% 0%, rgba(32, 63, 91, 0.24), transparent 34%),
                #0a192b;
        }

        .subject-catalog-heading {
            margin-bottom: 23px;
            padding-bottom: 17px;
            border-bottom: 1px solid #26374b;
        }

        .subject-catalog-heading .section-eyebrow {
            color: #78c936;
        }

        .subject-catalog-heading h1,
        .subject-catalog-heading h2 {
            margin-top: 5px;
            color: white;
            font-family: Georgia, "Times New Roman", serif;
            font-size: clamp(1.55rem, 3vw, 2.15rem);
            font-weight: 650;
            letter-spacing: -0.025em;
        }

        .subject-catalog-heading p {
            max-width: 720px;
            margin-top: 6px;
            color: #aab8c7;
            font-size: 0.88rem;
        }

        .mock-exam-banner {
            display: grid;
            gap: 4px;
            margin-top: 18px;
            padding: 18px 20px;
            border: 1px solid #147d78;
            border-left-width: 6px;
            border-radius: 14px;
            background: #f1f7f7;
            color: #203344;
            text-decoration: none;
        }
        .mock-exam-banner strong { font-size: 1.15rem; color: #18324b; }
        .mock-exam-banner:hover, .mock-exam-banner:focus-visible { background: #e4f1f0; }

        .subject-chapter-grid {
            display: grid;
            grid-template-columns: repeat(2, minmax(0, 1fr));
            gap: 13px;
        }

        .subject-chapter-card {
            display: flex;
            min-height: 158px;
            min-width: 0;
            flex-direction: column;
            justify-content: space-between;
            padding: 16px;
            border: 1px solid #2c3d51;
            border-radius: 12px;
            background: linear-gradient(145deg, #10223a, #0d1b2e);
            color: white;
            text-decoration: none;
            transition: border-color 0.18s ease, transform 0.18s ease, box-shadow 0.18s ease;
        }

        .subject-chapter-card:hover {
            transform: translateY(-2px);
            border-color: #78c936;
            box-shadow: 0 12px 26px -18px rgba(120, 201, 54, 0.6);
        }

        .subject-chapter-label {
            color: #83d249;
            font-size: 0.66rem;
            font-weight: 800;
            letter-spacing: 0.08em;
            text-transform: uppercase;
        }

        .subject-chapter-card h3 {
            margin-top: 9px;
            font-family: Georgia, "Times New Roman", serif;
            font-size: 1rem;
            line-height: 1.35;
        }

        .subject-chapter-card p {
            margin-top: 6px;
            color: #aab8c7;
            font-size: 0.75rem;
        }

        .subject-chapter-card-footer {
            display: flex;
            justify-content: space-between;
            gap: 8px;
            margin-top: 14px;
            padding-top: 10px;
            border-top: 1px solid #26374b;
            color: #b7c5d2;
            font-size: 0.72rem;
        }

        .subject-chapter-card-footer strong {
            color: #83d249;
        }

        .subject-coming-soon {
            margin-top: 18px;
            padding: 13px 15px;
            border: 1px solid #2a3a4d;
            border-radius: 10px;
            background: rgba(8, 18, 32, 0.6);
            color: #aab8c7;
            font-size: 0.82rem;
        }

        .workspace-breadcrumb {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            gap: 7px;
            margin: 0;
            padding-top: 12px;
            border-top: 1px solid #e8edf0;
            color: var(--neutral-muted);
            font-size: 0.8rem;
        }

        .workspace-breadcrumb > span:last-child {
            padding: 3px 8px;
            border-radius: 6px;
            background: var(--neutral-light);
            color: var(--neutral-dark);
            font-weight: 700;
        }

        .workspace-breadcrumb a {
            color: var(--primary);
            font-weight: 750;
            text-decoration: none;
        }

        .workspace-breadcrumb a:hover {
            text-decoration: underline;
        }

        /* Progress Bar */
        .progress-container {
            background: white;
            border-radius: 12px;
            padding: 16px 24px;
            margin-bottom: 24px;
            box-shadow: var(--card-shadow);
            border: 1px solid var(--border-color);
        }

        .progress-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            font-size: 0.85rem;
            font-weight: 600;
            color: var(--neutral-muted);
            margin-bottom: 8px;
        }

        .progress-track {
            height: 10px;
            background: #e2e8f0;
            border-radius: 10px;
            overflow: hidden;
        }

        .progress-bar {
            height: 100%;
            background: linear-gradient(90deg, var(--primary), var(--secondary));
            width: 2%;
            transition: width 0.4s ease;
        }

        .question-jump {
            background: white;
            border-radius: 12px;
            padding: 16px 18px;
            margin-bottom: 24px;
            box-shadow: var(--card-shadow);
            border: 1px solid var(--border-color);
        }

        .bank-card {
            background: white;
            border-radius: var(--radius);
            padding: 0 34px 34px;
            box-shadow: var(--card-shadow);
            border: 1px solid var(--border-color);
            margin-bottom: 24px;
            overflow: visible;
        }

        .bank-heading {
            margin: 0 0 18px;
        }

        .bank-heading h2 {
            font-size: 1.4rem;
            letter-spacing: -0.025em;
            margin-bottom: 5px;
        }

        .bank-heading p,
        .objective-description {
            color: var(--neutral-muted);
            font-size: 0.9rem;
        }

        .bank-hero {
            position: relative;
            margin: 0 -34px 34px;
            padding: clamp(30px, 5vw, 56px) 34px;
            border-radius: var(--radius) var(--radius) 0 0;
            color: white;
            background:
                radial-gradient(ellipse at 82% 18%, rgba(35, 73, 113, 0.3), transparent 38%),
                linear-gradient(118deg, #071629 0%, #0c2340 100%);
        }

        .bank-hero::after {
            content: "∠";
            position: absolute;
            right: clamp(24px, 7vw, 86px);
            top: 50%;
            transform: translateY(-56%) rotate(-12deg);
            color: rgba(255, 255, 255, 0.09);
            font-family: Georgia, serif;
            font-size: clamp(8rem, 19vw, 16rem);
            line-height: 1;
            pointer-events: none;
        }

        .bank-hero.chapter13-hero::after {
            content: none;
        }

        .bank-hero-layout {
            position: relative;
            z-index: 1;
            display: grid;
            grid-template-columns: minmax(0, 1fr);
        }

        .bank-hero.chapter13-hero .bank-hero-layout {
            grid-template-columns: minmax(0, 1.65fr) minmax(250px, 0.7fr);
            align-items: center;
            gap: clamp(28px, 5vw, 72px);
        }

        .bank-hero-content {
            position: relative;
            z-index: 1;
            max-width: 660px;
        }

        .bank-eyebrow,
        .section-eyebrow {
            font-size: 0.74rem;
            font-weight: 800;
            letter-spacing: 0.14em;
            text-transform: uppercase;
        }

        .bank-eyebrow {
            color: #78cf39;
        }

        .section-eyebrow {
            color: var(--secondary);
        }

        .bank-hero h1,
        .bank-hero h2 {
            max-width: 760px;
            margin: 10px 0 12px;
            color: white;
            font-family: Georgia, "Times New Roman", serif;
            font-size: clamp(2.15rem, 5vw, 3.65rem);
            font-weight: 600;
            letter-spacing: -0.045em;
            line-height: 1.08;
        }

        .bank-hero-description {
            max-width: 590px;
            color: #e0e9ed;
            font-size: 1.02rem;
        }

        .bank-hero.chapter13-hero .learning-outcomes li::before {
            color: #78c936;
        }

        .chapter13-hero-visual {
            display: flex;
            min-height: 270px;
            flex-direction: column;
            justify-content: center;
            align-items: center;
            padding: 22px;
            border: 1px solid rgba(201, 215, 229, 0.18);
            border-radius: 20px;
            background: rgba(8, 24, 43, 0.62);
        }

        .chapter13-hero-visual[hidden] {
            display: none;
        }

        .chapter13-hero-visual svg {
            width: min(100%, 300px);
            height: auto;
        }

        .chapter13-hero-visual figcaption {
            margin-top: 12px;
            color: #cbd6e2;
            font-family: Georgia, "Times New Roman", serif;
            font-size: 0.94rem;
            font-style: italic;
            font-weight: 600;
            text-align: center;
        }

        .learning-outcomes {
            display: grid;
            grid-template-columns: repeat(2, minmax(0, 1fr));
            gap: 8px 18px;
            max-width: 710px;
            margin-top: 20px;
            padding: 0;
            list-style: none;
        }

        .learning-outcomes li {
            display: flex;
            align-items: flex-start;
            gap: 9px;
            color: #f0f5f7;
            font-size: 0.9rem;
        }

        .learning-outcomes li::before {
            content: "✓";
            flex: 0 0 auto;
            color: #d9b66f;
            font-weight: 800;
        }

        .learning-navigation {
            position: sticky;
            top: 12px;
            z-index: 5;
            display: flex;
            flex-wrap: wrap;
            gap: 8px;
            margin: -8px 0 24px;
            padding: 10px;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            background: rgba(255, 255, 255, 0.96);
            box-shadow: 0 8px 22px -18px rgba(24, 50, 75, 0.6);
            backdrop-filter: blur(8px);
        }

        .learning-navigation .chapter13-tab-button {
            padding: 7px 11px;
            border-radius: 8px;
            color: var(--primary);
            border: 0;
            background: transparent;
            font: inherit;
            font-size: 0.82rem;
            font-weight: 700;
            white-space: nowrap;
            cursor: pointer;
        }

        .learning-navigation .chapter13-tab-button:hover,
        .learning-navigation .chapter13-tab-button:focus-visible {
            background: var(--primary-light);
        }

        .learning-navigation .chapter13-tab-button:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 2px;
        }

        .learning-navigation .chapter13-tab-button[aria-selected="true"] {
            background: var(--primary);
            color: white;
            box-shadow: 0 4px 12px rgba(24, 50, 75, 0.15);
        }

        .chapter13-tab-panel[hidden] {
            display: none;
        }

        .chapter13-panel-card {
            padding: clamp(18px, 3vw, 30px);
            border: 1px solid var(--border-color);
            border-radius: 16px;
            background: white;
            box-shadow: var(--card-shadow);
        }

        .chapter13-panel-heading {
            margin-bottom: 20px;
            padding-bottom: 14px;
            border-bottom: 1px solid var(--border-color);
        }

        .chapter13-panel-heading h3 {
            margin-top: 4px;
            color: var(--primary);
            font-family: Georgia, "Times New Roman", serif;
            font-size: clamp(1.35rem, 3vw, 1.8rem);
            font-weight: 650;
        }

        .chapter13-panel-heading p {
            margin-top: 5px;
            color: var(--neutral-muted);
            font-size: 0.9rem;
        }

        .chapter13-prerequisite-box {
            margin-top: 16px;
        }

        .chapter13-guide-callout {
            margin-top: 14px;
        }

        .chapter13-calculator-notes {
            margin-top: 14px;
        }

        .chapter13-tool-grid {
            display: grid;
            grid-template-columns: repeat(2, minmax(0, 1fr));
            align-items: start;
            gap: 16px;
        }

        .chapter13-prerequisite-grid {
            display: grid;
            grid-template-columns: minmax(0, 7fr) minmax(0, 5fr);
            align-items: start;
            gap: 16px;
        }

        .chapter13-prerequisite-column {
            display: grid;
            gap: 16px;
            min-width: 0;
        }

        .chapter13-prerequisite-column .chapter13-prerequisite-box {
            margin: 0;
        }

        .chapter13-tool {
            min-width: 0;
            padding: 18px;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            background: #f8fafc;
        }

        .chapter13-tool h4 {
            color: var(--primary);
            font-family: Georgia, "Times New Roman", serif;
            font-size: 1.05rem;
        }

        .chapter13-tool > p {
            margin: 6px 0 14px;
            color: var(--neutral-muted);
            font-size: 0.83rem;
        }

        .triangle-classification-groups {
            display: grid;
            gap: 12px;
        }

        .triangle-classification-group h5 {
            margin-bottom: 7px;
            color: var(--neutral-dark);
            font-size: 0.8rem;
        }

        .triangle-type-list {
            display: grid;
            gap: 7px;
        }

        .triangle-type-item {
            display: grid;
            grid-template-columns: 48px minmax(0, 1fr);
            align-items: center;
            gap: 10px;
            padding: 8px;
            border: 1px solid var(--border-color);
            border-radius: 9px;
            background: white;
        }

        .triangle-type-item svg {
            width: 48px;
            height: 42px;
            overflow: visible;
        }

        .triangle-type-item svg line,
        .triangle-type-item svg path,
        .triangle-type-item svg rect {
            fill: none;
            stroke: var(--secondary);
            stroke-linecap: round;
            stroke-linejoin: round;
            stroke-width: 2;
        }

        .triangle-type-item strong {
            display: block;
            color: var(--primary);
            font-size: 0.78rem;
        }

        .triangle-type-item span {
            display: block;
            color: var(--neutral-muted);
            font-size: 0.72rem;
            line-height: 1.4;
        }

        .triangle-classification-note {
            margin-top: 10px;
            color: var(--neutral-muted);
            font-size: 0.75rem;
        }

        .chapter13-tool-form {
            display: grid;
            gap: 10px;
        }

        .chapter13-tool-form label {
            display: grid;
            gap: 5px;
            color: var(--neutral-dark);
            font-size: 0.82rem;
            font-weight: 700;
        }

        .chapter13-tool-form input,
        .chapter13-tool-form select {
            width: 100%;
            min-height: 42px;
            padding: 8px 10px;
            border: 1px solid #cbd5dc;
            border-radius: 8px;
            background: white;
            color: var(--neutral-dark);
            font: inherit;
        }

        .chapter13-tool-form input:focus-visible,
        .chapter13-tool-form select:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 2px;
        }

        .chapter13-tool-action {
            min-height: 42px;
            padding: 9px 14px;
            border: 0;
            border-radius: 8px;
            background: var(--primary);
            color: white;
            font: inherit;
            font-size: 0.84rem;
            font-weight: 750;
            cursor: pointer;
        }

        .chapter13-tool-action:hover {
            background: var(--primary-hover);
        }

        .chapter13-tool-result {
            min-height: 42px;
            margin-top: 12px;
            padding: 10px 12px;
            border: 1px solid #cbd9e5;
            border-radius: 8px;
            background: white;
            color: var(--neutral-dark);
            font-size: 0.85rem;
            line-height: 1.5;
        }

        .chapter13-tool-result[hidden] {
            display: none;
        }

        .chapter13-tool-result.error {
            border-color: #fecaca;
            background: #fff0ef;
            color: #991b1b;
        }

        .triangle-lab-layout {
            display: grid;
            grid-template-columns: minmax(0, 0.9fr) minmax(0, 1.1fr);
            gap: 18px;
            align-items: center;
        }

        .triangle-lab-controls {
            display: grid;
            gap: 16px;
            padding: 16px;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            background: var(--neutral-light);
        }

        .triangle-lab-angle-controls {
            display: flex;
            flex-wrap: wrap;
            gap: 8px;
        }

        .triangle-lab-angle-button {
            min-height: 36px;
            padding: 7px 10px;
            border: 1px solid var(--border-color);
            border-radius: 8px;
            background: white;
            color: var(--primary);
            font: inherit;
            font-size: 0.78rem;
            font-weight: 700;
            cursor: pointer;
        }

        .triangle-lab-angle-button[aria-pressed="true"] {
            border-color: var(--primary);
            background: var(--primary);
            color: white;
        }

        .triangle-lab-angle-button:focus-visible {
            outline: 3px solid var(--secondary);
            outline-offset: 2px;
        }

        .triangle-lab-controls label {
            display: flex;
            justify-content: space-between;
            gap: 12px;
            color: var(--neutral-dark);
            font-size: 0.83rem;
            font-weight: 700;
        }

        .triangle-lab-controls input[type="range"] {
            width: 100%;
            margin-top: 8px;
            accent-color: var(--secondary);
        }

        .triangle-lab-readout {
            display: grid;
            gap: 8px;
            padding: 14px;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: white;
            font-size: 0.82rem;
        }

        .triangle-lab-readout div {
            display: flex;
            justify-content: space-between;
            gap: 12px;
        }

        .triangle-lab-visual {
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 280px;
            padding: 16px;
            border-radius: 12px;
            background: var(--primary);
        }

        .triangle-lab-visual svg {
            width: min(100%, 390px);
            height: auto;
        }

        .calculator-tip-grid {
            display: grid;
            grid-template-columns: repeat(2, minmax(0, 1fr));
            gap: 14px;
            margin-top: 18px;
        }

        .calculator-tip-grid .calculator-pitfall {
            font-size: 0.88rem;
        }

        .chapter13-quiz-card {
            padding: clamp(20px, 4vw, 34px);
            border: 1px solid #304658;
            border-radius: 16px;
            background: linear-gradient(135deg, #10283e, #18324b);
            color: white;
            box-shadow: var(--card-shadow);
        }

        .chapter13-quiz-card h3 {
            margin: 6px 0 8px;
            font-family: Georgia, "Times New Roman", serif;
            font-size: clamp(1.4rem, 3vw, 2rem);
        }

        .chapter13-quiz-card p {
            color: #e0e9ed;
            font-size: 0.92rem;
        }

        .chapter13-quiz-card .btn {
            margin-top: 18px;
            background: #d9b66f;
            color: #203344;
        }

        .chapter13-quiz-card .btn:hover {
            background: #e5c987;
        }

        .chapter13-random-quiz {
            display: grid;
            grid-template-columns: minmax(190px, 1fr) auto;
            gap: 8px 12px;
            align-items: end;
            max-width: 500px;
            margin-top: 20px;
            padding: 10px 12px;
            border: 1px solid rgba(223, 233, 239, 0.2);
            border-radius: 14px;
            background: rgba(7, 22, 41, 0.58);
        }

        .chapter13-random-quiz label {
            display: flex;
            align-items: center;
            flex-wrap: wrap;
            gap: 9px;
            color: #e5edf2;
            font-size: 0.9rem;
            font-weight: 650;
        }

        .chapter13-random-quiz input {
            width: 96px;
            min-height: 40px;
            padding: 7px 10px;
            border: 1px solid #53677d;
            border-radius: 8px;
            outline: none;
            background: #1c2a3c;
            color: #80d23d;
            font: inherit;
            font-weight: 800;
            text-align: center;
        }

        .chapter13-random-quiz input:focus-visible {
            outline: 3px solid #d9b66f;
            outline-offset: 2px;
        }

        .chapter13-random-quiz button {
            min-height: 40px;
            padding: 8px 18px;
            border: 0;
            border-radius: 8px;
            background: #78c936;
            color: #10220a;
            font: inherit;
            font-weight: 800;
            cursor: pointer;
        }

        .chapter13-random-quiz button:hover {
            background: #91dc51;
        }

        .chapter13-random-quiz button:focus-visible {
            outline: 3px solid #d9b66f;
            outline-offset: 2px;
        }

        .chapter13-random-quiz-hint,
        .chapter13-random-quiz-error {
            grid-column: 1 / -1;
            color: #cbd6e2;
            font-size: 0.78rem;
        }

        .chapter13-random-quiz-error {
            color: #fecaca;
        }

        .chapter13-random-quiz-error:empty {
            display: none;
        }

        .chapter13-learning-guide {
            margin: 0 0 34px;
            scroll-margin-top: 84px;
        }

        .chapter13-guide-content {
            display: grid;
            gap: 18px;
            padding: clamp(16px, 3vw, 30px);
            border: 1px solid #26384d;
            border-radius: 20px;
            background: #071629;
            color: #f0f5f7;
        }

        .chapter13-guide-objective {
            display: grid;
            gap: 16px;
            min-width: 0;
            padding: clamp(16px, 2.5vw, 26px);
            border: 1px solid #26384d;
            border-radius: 16px;
            background: #0c1d32;
        }

        .chapter13-guide-objective-heading {
            display: flex;
            align-items: flex-start;
            gap: 12px;
        }

        .chapter13-guide-objective-number {
            flex: 0 0 auto;
            padding: 4px 10px;
            border: 1px solid rgba(16, 185, 129, 0.4);
            border-radius: 999px;
            background: rgba(16, 185, 129, 0.12);
            color: #34d399;
            font-size: 0.68rem;
            font-weight: 800;
            letter-spacing: 0.04em;
            text-transform: uppercase;
        }

        .chapter13-guide-objective h3 {
            color: white;
            font-family: Georgia, "Times New Roman", serif;
            font-size: clamp(1.05rem, 2.5vw, 1.4rem);
            font-weight: 700;
            line-height: 1.35;
        }

        .chapter13-guide-objective > p {
            color: #cbd6e2;
            font-size: 0.9rem;
            line-height: 1.65;
        }

        .chapter13-guide-card-grid {
            display: grid;
            grid-template-columns: repeat(3, minmax(0, 1fr));
            gap: 12px;
        }

        .chapter13-guide-card-grid.two-columns {
            grid-template-columns: repeat(2, minmax(0, 1fr));
        }

        .chapter13-guide-card {
            min-width: 0;
            padding: 14px;
            border: 1px solid #263448;
            border-radius: 12px;
            background: #071221;
            color: #e7edf3;
            font-size: 0.86rem;
            line-height: 1.55;
        }

        .chapter13-guide-diagram {
            margin-top: 14px;
            padding: 10px;
            border: 1px solid #1b2a3f;
            border-radius: 9px;
            background: #080d16;
        }

        .chapter13-guide-diagram svg {
            display: block;
            width: 100%;
            max-height: 190px;
        }

        .chapter13-guide-objective-note {
            display: grid;
            grid-template-columns: auto minmax(0, 1fr);
            align-items: start;
            gap: 12px;
            padding: 16px;
            border: 1px solid #263448;
            border-radius: 12px;
            background: #071221;
            color: #cbd6e2;
            font-size: 0.88rem;
            line-height: 1.6;
        }

        .chapter13-guide-objective-note strong {
            color: #34d399;
        }

        .chapter13-guide-card h4 {
            margin-bottom: 6px;
            color: var(--guide-accent, #34d399);
            font-size: 0.92rem;
            font-weight: 800;
        }

        .chapter13-guide-card p + p {
            margin-top: 8px;
        }

        .chapter13-guide-card .guide-formula {
            color: #e7edf3;
            font-size: 0.91rem;
            overflow-wrap: anywhere;
        }

        .chapter13-guide-card .guide-formula + .guide-formula {
            margin-top: 10px;
        }

        .chapter13-guide-role-hypotenuse {
            --guide-accent: var(--side-hypotenuse);
        }

        .chapter13-guide-role-opposite {
            --guide-accent: #34d399;
        }

        .chapter13-guide-role-adjacent {
            --guide-accent: #fb923c;
        }

        .chapter13-guide-card .triangle-role-hypotenuse {
            color: #60a5fa;
        }

        .chapter13-guide-card .triangle-role-opposite {
            color: #34d399;
        }

        .chapter13-guide-card .triangle-role-adjacent {
            color: #fb923c;
        }

        .objective4-trig-grid {
            gap: 16px;
        }

        .objective4-card {
            display: flex;
            flex-direction: column;
            gap: 10px;
            padding: 18px;
        }

        .objective4-card h4 {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            gap: 8px;
            color: #34d399;
            font-size: 1rem;
        }

        .objective4-card h4 .objective4-mnemonic {
            color: #cbd6e2;
            font-size: 0.84rem;
            font-weight: 600;
        }

        .objective4-middle-letter {
            color: #ef4444;
            font-weight: 800;
        }

        .objective4-last-letter {
            color: #38bdf8;
            font-weight: 800;
        }

        .objective4-card .guide-formula {
            margin: 0;
            padding: 10px 12px;
            border: 1px solid #263448;
            border-radius: 9px;
            background: #071221;
            font-size: 0.9rem;
            overflow-x: auto;
        }

        .objective4-pythagorean-card {
            gap: 7px;
        }

        .objective4-pythagorean-card .guide-formula {
            display: flex;
            flex-wrap: wrap;
            align-items: baseline;
            gap: 4px 12px;
            padding: 7px 12px;
        }

        .objective4-pythagorean-card .guide-formula + .guide-formula {
            margin-top: 0;
        }

        .objective4-pythagorean-card .formula-label {
            color: #cbd6e2;
            font-size: 0.8rem;
            font-weight: 700;
        }

        .objective4-pythagorean-grid {
            grid-template-columns: repeat(2, minmax(0, 1fr));
        }

        .objective4-steps {
            margin: 0;
            padding: 14px 18px 0 34px;
            border-top: 1px solid #26384d;
            color: #cbd6e2;
            font-size: 0.88rem;
            line-height: 1.65;
        }

        .objective4-steps li + li {
            margin-top: 5px;
        }

        .chapter13-learning-guide[hidden],
        .learning-navigation[hidden],
        .learning-outcomes[hidden] {
            display: none;
        }

        .lesson-guide-heading {
            margin-bottom: 16px;
        }

        .lesson-guide-heading h2 {
            margin-top: 4px;
            color: var(--primary);
            font-family: Georgia, "Times New Roman", serif;
            font-size: 1.8rem;
            font-weight: 600;
            letter-spacing: -0.025em;
        }

        .lesson-guide-heading p {
            margin-top: 5px;
            color: var(--neutral-muted);
            font-size: 0.92rem;
        }

        .prerequisite-box {
            margin-bottom: 14px;
            border: 1px solid #cbd9e5;
            border-radius: 12px;
            background: #f4f7fa;
            scroll-margin-top: 84px;
        }

        .prerequisite-box summary {
            padding: 14px 16px;
            color: var(--primary);
            cursor: pointer;
            font-weight: 750;
        }

        .prerequisite-content {
            padding: 0 16px 16px;
            color: var(--neutral-dark);
            font-size: 0.9rem;
        }

        .prerequisite-content p + p {
            margin-top: 8px;
        }

        .prerequisite-content .math-callout {
            margin: 10px 0;
            padding: 10px 12px;
            border-left: 3px solid var(--primary);
            border-radius: 0 8px 8px 0;
            background: white;
        }

        .chapter13-reference-section {
            margin-bottom: 14px;
            padding: 18px;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            background: white;
            scroll-margin-top: 84px;
        }

        .chapter13-reference-section > h3 {
            color: var(--primary);
            font-family: Georgia, "Times New Roman", serif;
            font-size: 1.28rem;
            font-weight: 650;
        }

        .chapter13-reference-section > p {
            margin-top: 5px;
            color: var(--neutral-muted);
            font-size: 0.88rem;
        }

        .reference-angle-lab {
            display: grid;
            grid-template-columns: minmax(0, 1.05fr) minmax(0, 0.95fr);
            gap: 18px;
            margin-top: 14px;
        }

        .reference-triangle-card {
            min-width: 0;
            padding: 14px;
            border-radius: 12px;
            background: var(--primary);
            color: white;
        }

        .reference-angle-controls {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            gap: 8px;
            margin-bottom: 8px;
        }

        .reference-angle-controls > span {
            margin-right: auto;
            color: #e0e9ed;
            font-size: 0.82rem;
            font-weight: 650;
        }

        .reference-angle-button {
            min-height: 38px;
            padding: 7px 10px;
            border: 1px solid rgba(255, 255, 255, 0.3);
            border-radius: 8px;
            background: rgba(255, 255, 255, 0.08);
            color: white;
            font: inherit;
            font-size: 0.78rem;
            font-weight: 700;
            cursor: pointer;
        }

        .reference-angle-button[aria-pressed="true"] {
            border-color: #d9b66f;
            background: #d9b66f;
            color: #203344;
        }

        .reference-angle-button:focus-visible {
            outline: 3px solid white;
            outline-offset: 2px;
        }

        .reference-triangle-diagram {
            display: block;
            width: min(100%, 390px);
            height: auto;
            margin: 0 auto;
        }

        .reference-triangle-diagram .side-hypotenuse,
        .reference-triangle-diagram .side-opposite,
        .reference-triangle-diagram .side-adjacent {
            fill: none;
            stroke-width: 5;
            stroke-linecap: round;
            transition: stroke 0.2s ease;
        }

        .reference-triangle-diagram .side-hypotenuse {
            stroke: var(--side-hypotenuse);
        }

        .reference-triangle-diagram .side-opposite {
            stroke: var(--side-opposite);
        }

        .reference-triangle-diagram .side-adjacent {
            stroke: var(--side-adjacent);
        }

        .reference-triangle-diagram .side-label-hypotenuse {
            fill: #93c5fd;
        }

        .reference-triangle-diagram .side-label-opposite {
            fill: #86efac;
        }

        .reference-triangle-diagram .side-label-adjacent {
            fill: #fdba74;
        }

        #reference-angle-a-marker,
        #reference-angle-b-marker {
            stroke: #d9b66f;
            stroke-width: 2.5;
        }

        #reference-angle-a-marker {
            display: block;
        }

        #reference-angle-b-marker {
            display: none;
        }

        .reference-side-key {
            display: grid;
            grid-template-columns: repeat(3, minmax(0, 1fr));
            gap: 6px;
            margin-top: 8px;
        }

        .reference-side-key > div {
            padding: 8px 5px;
            border: 1px solid rgba(255, 255, 255, 0.12);
            border-radius: 8px;
            background: rgba(255, 255, 255, 0.06);
            text-align: center;
        }

        .reference-side-key strong,
        .reference-side-key span {
            display: block;
        }

        .reference-side-key strong {
            font-size: 0.73rem;
        }

        .reference-side-key span {
            margin-top: 3px;
            color: #d8e1e8;
            font-size: 0.68rem;
        }

        .reference-formulas {
            display: grid;
            align-content: start;
            gap: 9px;
        }

        .reference-formula-card {
            padding: 12px;
            border: 1px solid var(--border-color);
            border-left: 4px solid var(--secondary);
            border-radius: 9px;
            background: #f8fafc;
        }

        .reference-formula-card:nth-child(2) {
            border-left-color: var(--side-hypotenuse);
        }

        .reference-formula-card:nth-child(3) {
            border-left-color: var(--side-adjacent);
        }

        .reference-formula-card > strong {
            display: block;
            margin-bottom: 5px;
            color: var(--primary);
            font-size: 0.82rem;
        }

        .reference-formula-card > div {
            min-height: 28px;
            font-size: 0.88rem;
        }

        .reference-triangle-status {
            min-height: 1.4em;
            margin-top: 9px;
            color: #e0e9ed;
            font-size: 0.8rem;
        }

        .special-triangle-grid {
            display: grid;
            grid-template-columns: repeat(2, minmax(0, 1fr));
            gap: 12px;
            margin-top: 14px;
        }

        .special-triangle-card {
            padding: 14px;
            border: 1px solid #cbd9e5;
            border-radius: 10px;
            background: #f4f7fa;
        }

        .special-triangle-card h4 {
            color: var(--primary);
            font-size: 0.9rem;
        }

        .special-triangle-card p {
            margin-top: 5px;
            color: var(--neutral-muted);
            font-size: 0.82rem;
        }

        .special-triangle-ratios {
            margin-top: 9px;
            color: var(--neutral-dark);
            font-size: 0.86rem;
            font-weight: 650;
        }

        .special-ratio-table {
            width: 100%;
            margin-top: 14px;
            border-collapse: collapse;
            font-size: 0.84rem;
            text-align: center;
        }

        .special-ratio-table th,
        .special-ratio-table td {
            padding: 8px 6px;
            border: 1px solid var(--border-color);
        }

        .special-ratio-table th {
            background: var(--primary-light);
            color: var(--primary);
        }

        .calculator-pitfalls {
            display: grid;
            grid-template-columns: repeat(2, minmax(0, 1fr));
            gap: 10px;
            margin-top: 14px;
        }

        .calculator-pitfall {
            padding: 12px;
            border: 1px solid #f0dfb8;
            border-radius: 9px;
            background: #fffaf0;
            color: #604a14;
            font-size: 0.84rem;
        }

        .calculator-pitfall strong {
            display: block;
            margin-bottom: 4px;
            color: #48370f;
        }

        .lesson-topic-list {
            display: grid;
            gap: 12px;
        }

        .lesson-topic {
            overflow: hidden;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            background: white;
            scroll-margin-top: 84px;
        }

        .lesson-topic > summary {
            padding: 14px 16px;
            background: var(--primary);
            color: white;
            cursor: pointer;
            font-weight: 750;
            list-style-position: inside;
        }

        .lesson-topic[open] > summary {
            border-bottom: 1px solid var(--border-color);
        }

        .lesson-topic-content {
            padding: 16px;
        }

        .lesson-tabs {
            display: flex;
            gap: 6px;
            margin-bottom: 14px;
            padding: 4px;
            border-radius: 10px;
            background: var(--neutral-light);
        }

        .lesson-tab {
            min-height: 40px;
            flex: 1 1 0;
            padding: 8px 12px;
            border: 0;
            border-radius: 8px;
            background: transparent;
            color: var(--neutral-muted);
            font: inherit;
            font-size: 0.86rem;
            font-weight: 700;
            cursor: pointer;
        }

        .lesson-tab[aria-selected="true"] {
            background: white;
            color: var(--primary);
            box-shadow: 0 2px 8px rgba(24, 50, 75, 0.1);
        }

        .lesson-tab:focus-visible,
        .worked-step-toggle:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 2px;
        }

        .objective-card-wrap {
            display: flex;
            flex-direction: column;
            gap: 6px;
        }

        .objective-card-wrap > .objective-card {
            flex: 1 1 auto;
        }

        .objective-video-embed {
            width: 100%;
        }

        .objective-video-embed iframe {
            display: block;
            width: 100%;
            aspect-ratio: 16 / 9;
            border: 0;
            border-radius: 10px;
        }

        .objective-watch {
            align-self: flex-start;
            padding: 6px 12px;
            border: 0;
            border-radius: 999px;
            background: #fdecec;
            color: #b3261e;
            font-size: 0.82rem;
            font-weight: 700;
            cursor: pointer;
            text-decoration: none;
        }

        .objective-watch:hover,
        .objective-watch:focus-visible {
            background: #f9d4d2;
            outline: 2px solid #c99d4e;
        }

        .lesson-video-list {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(min(100%, 260px), 1fr));
            gap: 14px;
        }

        .lesson-video {
            display: flex;
            flex-direction: column;
            gap: 6px;
            min-width: 0;
            overflow-wrap: anywhere;
        }

        .lesson-video-play,
        .lesson-video iframe {
            width: 100%;
            aspect-ratio: 16 / 9;
            border: 0;
            border-radius: 10px;
        }

        .lesson-video-play {
            display: flex;
            align-items: center;
            justify-content: center;
            background-color: #18324b;
            background-size: cover;
            background-position: center;
            color: white;
            font-size: 2rem;
            cursor: pointer;
            text-decoration: none;
        }

        .lesson-video-play span {
            padding: 6px 18px;
            border-radius: 12px;
            background: rgba(179, 38, 30, 0.92);
        }

        .lesson-video-play:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 2px;
        }

        .lesson-video-fullscreen {
            display: none;
            align-self: flex-start;
            min-height: 44px;
            padding: 6px 12px;
            border: 1px solid #e8b6b3;
            border-radius: 8px;
            background: #fdecec;
            color: #b3261e;
            font-size: 0.84rem;
            font-weight: 700;
            cursor: pointer;
        }

        .lesson-video-fullscreen:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 2px;
        }

        @media (max-width: 520px) {
            .lesson-video-fullscreen:not([hidden]) {
                display: inline-flex;
                align-items: center;
            }
        }

        .lesson-video-youtube {
            align-self: flex-start;
            display: inline-flex;
            align-items: center;
            min-height: 44px;
            padding: 0;
            border: 0;
            background: transparent;
            color: #b3261e;
            font: inherit;
            font-size: 0.84rem;
            font-weight: 700;
            text-decoration: underline;
            cursor: pointer;
        }

        .lesson-video-youtube:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 2px;
        }

        .lesson-panel {
            color: var(--neutral-dark);
            font-size: 0.92rem;
            line-height: 1.65;
        }

        .lesson-panel[hidden] {
            display: none;
        }

        .lesson-panel p + p,
        .lesson-panel ul + p {
            margin-top: 10px;
        }

        .lesson-panel ul {
            padding-left: 1.3rem;
        }

        .lesson-concept-steps {
            display: grid;
            gap: 8px;
            margin: 0;
            padding-inline-start: 1.4rem;
        }

        .lesson-concept-steps li {
            padding-left: 3px;
        }

        .fx82 {
            max-width: 430px;
            margin: 0 auto;
            padding: 16px;
            border-radius: 20px;
            background: linear-gradient(160deg, #0f1f30, #08121d);
            border: 1px solid #27415a;
            box-shadow: 0 18px 40px -20px rgba(0, 0, 0, 0.6);
            color: #e8eef4;
        }

        .fx82-lcd {
            background: #cfe0cc;
            color: #14231a;
            border-radius: 10px;
            padding: 8px 12px;
            min-height: 128px;
            display: flex;
            flex-direction: column;
            justify-content: space-between;
            box-shadow: inset 0 2px 8px rgba(0, 0, 0, 0.35);
            font-family: "Courier New", monospace;
        }

        .fx82-indicators {
            display: flex;
            gap: 8px;
            font-size: 0.68rem;
            font-weight: 700;
            min-height: 14px;
        }

        .fx82-indicators span {
            background: rgba(20, 35, 26, 0.12);
            border-radius: 3px;
            padding: 0 4px;
        }

        .fx82-expr {
            font-size: 1.1rem;
            min-height: 44px;
            white-space: nowrap;
            overflow-x: auto;
            overflow-y: hidden;
            scrollbar-width: none;
        }

        .fx82-caret {
            display: inline-block;
            width: 2px;
            height: 1.1em;
            background: #14231a;
            vertical-align: text-bottom;
            animation: fx82-blink 1s steps(1) infinite;
        }

        @keyframes fx82-blink { 50% { opacity: 0; } }

        .fx82-result {
            text-align: right;
            font-size: 1.7rem;
            font-weight: 700;
            min-height: 36px;
            overflow-x: auto;
            white-space: nowrap;
        }

        .fx82-result.is-error { font-size: 1.2rem; color: #8b1d18; }

        .fx82-note {
            min-height: 20px;
            margin: 6px 2px 0;
            font-size: 0.78rem;
            color: #9fb4c6;
        }

        .fx82-frac {
            display: inline-flex;
            flex-direction: column;
            align-items: center;
            vertical-align: middle;
            margin: 0 3px;
            line-height: 1.15;
            font-size: 0.92em;
        }

        .fx82-frac-num {
            border-bottom: 2px solid currentColor;
            padding: 0 4px 1px;
            min-width: 1ch;
            text-align: center;
            white-space: nowrap;
        }

        .fx82-frac-den {
            padding: 1px 4px 0;
            min-width: 1ch;
            text-align: center;
            white-space: nowrap;
        }

        .fx82-whole { margin-right: 4px; }

        .fx82-sqrt {
            display: inline-flex;
            align-items: stretch;
            vertical-align: middle;
            margin: 0 2px;
        }

        .fx82-sqrt-sign {
            font-size: 1.25em;
            line-height: 1;
            align-self: flex-end;
            margin-right: -1px;
        }

        .fx82-sqrt-index {
            font-size: 0.6em;
            align-self: flex-start;
            margin-right: -4px;
        }

        .fx82-sqrt-body {
            border-top: 2px solid currentColor;
            padding: 1px 3px 0;
            min-width: 1ch;
            white-space: nowrap;
        }

        .fx82-box {
            display: inline-block;
            min-width: 0.9ch;
            opacity: 0.45;
        }

        .fx82-result .fx82-frac { font-size: 0.85em; }

        .fx82-menu,
        .fx82-stat {
            background: #0c1a28;
            border: 1px solid #27415a;
            border-radius: 12px;
            padding: 10px;
            margin: 8px 0;
            font-size: 0.82rem;
        }

        .fx82-menu[hidden], .fx82-stat[hidden] { display: none; }

        .fx82-menu-row,
        .fx82-stat-row {
            display: flex;
            flex-wrap: wrap;
            gap: 6px;
            margin-top: 8px;
            align-items: center;
        }

        .fx82-menu-row > span { width: 62px; color: #9fb4c6; }

        .fx82-menu button,
        .fx82-stat button {
            background: #17314a;
            color: #e8eef4;
            border: 1px solid #2c4b69;
            border-radius: 8px;
            padding: 5px 9px;
            font: inherit;
            cursor: pointer;
        }

        .fx82-menu button.is-active,
        .fx82-stat button.is-active { background: #147d78; border-color: #1fb3ab; }

        .fx82-stat-data {
            margin-top: 6px;
            color: #b9cad8;
            word-break: break-word;
            max-height: 64px;
            overflow-y: auto;
        }

        .fx82-keys {
            display: grid;
            grid-template-columns: repeat(5, 1fr);
            gap: 4px 8px;
            margin-top: 10px;
        }

        .fx82-keywrap {
            display: grid;
            grid-template-columns: 1fr 1fr;
            align-items: end;
            min-height: 52px;
        }

        .fx82-shift-label,
        .fx82-alpha-label {
            font-size: 0.64rem;
            font-weight: 700;
            line-height: 1.2;
            padding: 0 2px 2px;
        }

        .fx82-shift-label { color: #f2c14e; }
        .fx82-alpha-label { color: #ff7b72; text-align: right; }

        .fx82-key {
            grid-column: 1 / -1;
            min-height: 34px;
            border: 0;
            border-radius: 8px;
            font: inherit;
            font-size: 0.86rem;
            font-weight: 700;
            cursor: pointer;
            color: #f2f6fa;
            box-shadow: 0 3px 0 rgba(0, 0, 0, 0.45);
        }

        .fx82-key:active { transform: translateY(2px); box-shadow: 0 1px 0 rgba(0, 0, 0, 0.45); }
        .fx82-key:focus-visible { outline: 3px solid #c99d4e; outline-offset: 2px; }
        .fx82 .fx82-key-fn { background: #2b3f54; color: #f2f6fa; }
        .fx82 .fx82-key-num { background: #4a5f75; color: #f2f6fa; }
        .fx82 .fx82-key-op { background: #1f6fb5; color: #f2f6fa; }
        .fx82 .fx82-key-nav { background: #2b3f54; color: #f2f6fa; }
        .fx82 .fx82-key-del { background: #b0742a; color: #f2f6fa; }
        .fx82 .fx82-key-ac { background: #bd3b36; color: #f2f6fa; }
        .fx82 .fx82-key-eq { background: #147d78; color: #f2f6fa; }
        .fx82 .fx82-key-shift { background: #d9a627; color: #1b1b1b; }
        .fx82 .fx82-key-alpha { background: #d95c55; color: #f2f6fa; }
        .fx82 .fx82-key.is-on { outline: 3px solid #fff; }

        .solve-flow {
            list-style: none;
            margin: 14px 0 0;
            padding: 0;
            display: grid;
            gap: 0;
        }

        .solve-step {
            position: relative;
            display: grid;
            grid-template-columns: 34px 1fr;
            gap: 12px;
            padding-bottom: 16px;
        }

        .solve-step:not(:last-child)::before {
            content: "";
            position: absolute;
            left: 16px;
            top: 34px;
            bottom: 2px;
            width: 2px;
            background: #cbd5e1;
        }

        .solve-step-num {
            width: 34px;
            height: 34px;
            border-radius: 50%;
            background: #112233;
            color: #fff;
            font-weight: 700;
            display: flex;
            align-items: center;
            justify-content: center;
        }

        .solve-step-body {
            background: #f8fafc;
            border: 1px solid #e2e8f0;
            border-radius: 10px;
            padding: 10px 14px;
        }

        .solve-step-body > strong {
            display: block;
            color: #112233;
        }

        .solve-step-body p {
            margin: 4px 0 0;
        }

        .solve-formula-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
            gap: 10px;
            margin-top: 10px;
        }

        .solve-formula-card {
            background: #fff;
            border: 1px solid #e2e8f0;
            border-top: 4px solid var(--card-accent, #64748b);
            border-radius: 8px;
            padding: 8px 12px;
        }

        .solve-formula-card h4 {
            margin: 0 0 4px;
            font-size: 0.85rem;
            color: var(--card-accent, #334155);
        }

        .solve-formula-card div {
            padding: 3px 0;
            overflow-x: auto;
        }

        .triangle-side-key {
            display: flex;
            flex-wrap: wrap;
            gap: 8px 14px;
            margin: 12px 0;
            padding: 10px 12px;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: #f8fafc;
            font-size: 0.78rem;
            font-weight: 700;
        }

        .triangle-side-label {
            display: inline-flex;
            align-items: center;
            gap: 6px;
        }

        .triangle-side-label::before {
            width: 18px;
            height: 4px;
            border-radius: 999px;
            background: currentColor;
            content: "";
        }

        .triangle-role-hypotenuse {
            color: var(--side-hypotenuse);
        }

        .triangle-role-opposite {
            color: var(--side-opposite);
        }

        .triangle-role-adjacent {
            color: var(--side-adjacent);
        }

        .quiz-body .triangle-diagram .side-hypotenuse,
        .quiz-body .triangle-diagram .side-opposite,
        .quiz-body .triangle-diagram .side-adjacent {
            stroke: #334155;
        }

        .quiz-body .triangle-diagram .side-label-hypotenuse,
        .quiz-body .triangle-diagram .side-label-opposite,
        .quiz-body .triangle-diagram .side-label-adjacent {
            fill: #334155;
        }

        .solution-triangle-diagram {
            display: flex;
            justify-content: center;
            margin: 12px 0;
            padding: 10px;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: #f8fafc;
        }

        .solution-triangle-diagram svg {
            width: min(100%, 300px);
            height: auto;
            max-height: 260px;
        }

        .worked-example-question {
            margin-bottom: 12px;
            font-weight: 700;
        }

        .worked-example-diagram {
            display: flex;
            justify-content: center;
            margin: 10px 0;
            padding: 10px;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: #f8fafc;
        }

        .worked-example-diagram:empty {
            display: none;
        }

        .worked-example-diagram svg {
            width: min(100%, 300px);
            height: auto;
            max-height: 260px;
        }

        .worked-example-steps {
            margin-top: 12px;
            padding: 14px;
            border: 1px solid #cbd9e5;
            border-radius: 10px;
            background: #f4f7fa;
        }

        .worked-example-steps ol {
            margin: 10px 0 12px;
            padding-left: 1.35rem;
        }

        .worked-example-steps li + li {
            margin-top: 6px;
        }

        .solution-step-content {
            overflow-x: auto;
        }

        .solution-math {
            unicode-bidi: isolate;
        }

        .worked-example-steps li[hidden],
        .worked-example-answer[hidden] {
            display: none;
        }

        .worked-step-toggle {
            min-height: 40px;
            padding: 8px 12px;
            border: 1px solid var(--primary);
            border-radius: 8px;
            background: var(--primary);
            color: white;
            font: inherit;
            font-size: 0.84rem;
            font-weight: 700;
            cursor: pointer;
        }

        .worked-example-answer {
            margin-top: 10px;
            padding-top: 10px;
            border-top: 1px solid #cbd9e5;
            color: var(--primary);
            font-weight: 750;
        }

        .triangle-diagram .side-hypotenuse {
            stroke: var(--side-hypotenuse);
        }

        .triangle-diagram .side-opposite {
            stroke: var(--side-opposite);
        }

        .triangle-diagram .side-adjacent {
            stroke: var(--side-adjacent);
        }

        .triangle-diagram .side-label-hypotenuse {
            fill: var(--side-hypotenuse);
        }

        .triangle-diagram .side-label-opposite {
            fill: var(--side-opposite);
        }

        .triangle-diagram .side-label-adjacent {
            fill: var(--side-adjacent);
        }

        .practice-mode-switch {
            display: flex;
            flex-wrap: wrap;
            gap: 8px;
            margin: 0 0 20px;
        }

        .practice-mode-switch[hidden] { display: none; }

        .practice-mode-switch button {
            min-height: 44px;
            padding: 10px 18px;
            border: 1px solid var(--border-color);
            border-radius: 999px;
            background: white;
            color: var(--primary);
            font: inherit;
            font-weight: 750;
            cursor: pointer;
        }

        .practice-mode-switch button[aria-pressed="true"] {
            border-color: var(--primary);
            background: var(--primary);
            color: white;
        }

        .practice-mode-switch button:focus-visible {
            outline: 3px solid #d9b66f;
            outline-offset: 2px;
        }

        .test-launch-card {
            display: grid;
            gap: 20px;
            padding: clamp(22px, 4vw, 36px);
            border-color: #d3e2e4;
            background:
                radial-gradient(ellipse at 100% 0, rgba(20, 125, 120, 0.08), transparent 42%),
                #fff;
        }

        .test-launch-copy h3 {
            margin: 6px 0 8px;
            color: var(--primary);
            font-size: clamp(1.35rem, 3vw, 1.8rem);
            letter-spacing: -0.025em;
        }

        .test-launch-copy p {
            max-width: 700px;
            color: var(--neutral-muted);
        }

        .test-details {
            display: grid;
            grid-template-columns: repeat(3, minmax(0, 1fr));
            gap: 12px;
            margin: 0;
            padding: 0;
            list-style: none;
        }

        .test-details li {
            display: grid;
            align-content: start;
            gap: 4px;
            min-height: 82px;
            padding: 14px 16px;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            background: rgba(255, 255, 255, 0.88);
        }

        .test-details strong {
            color: var(--primary);
            font-size: 0.98rem;
        }

        .test-details span,
        .test-integrity-disclaimer {
            color: var(--neutral-muted);
            font-size: 0.84rem;
        }

        .test-integrity-disclaimer {
            margin: -8px 0 0;
        }

        .test-fullscreen-error {
            margin: 0;
            color: #8c2824;
            font-size: 0.9rem;
        }

        .test-launch-card #start-test-without-fullscreen {
            justify-self: start;
        }

        .test-launch-card #start-chapter-test {
            justify-self: start;
            min-height: 48px;
        }

        .test-launch-card #start-chapter-test:disabled {
            cursor: wait;
            opacity: 0.65;
        }

        .test-session-banner {
            display: flex;
            align-items: center;
            justify-content: space-between;
            gap: 18px;
            margin-bottom: 18px;
            padding: 16px 20px;
            border: 1px solid #cfe4e2;
            border-left: 4px solid var(--secondary);
            border-radius: 12px;
            background: #f0f8f7;
        }

        .test-session-banner[hidden] {
            display: none;
        }

        .test-session-label {
            color: var(--primary);
            font-size: 0.96rem;
            font-weight: 800;
        }

        .test-session-banner p {
            margin: 3px 0 0;
            color: var(--neutral-muted);
            font-size: 0.88rem;
        }

        .test-session-banner[data-state="warning"] {
            border-color: #f0d7a2;
            border-left-color: #c17b16;
            background: #fff9eb;
        }

        .test-session-exits {
            display: grid;
            flex: 0 0 auto;
            gap: 2px;
            justify-items: end;
        }

        .test-session-exits span {
            color: var(--neutral-muted);
            font-size: 0.76rem;
            font-weight: 650;
        }

        .test-session-exits strong {
            color: var(--primary);
            font-size: 1.15rem;
            font-variant-numeric: tabular-nums;
        }

        .test-fullscreen-pause {
            margin: 0 0 24px;
            padding: clamp(24px, 5vw, 40px);
            border: 1px solid #f0d7a2;
            border-radius: var(--radius);
            background: #fff9eb;
            box-shadow: var(--card-shadow);
            text-align: center;
        }

        .test-fullscreen-pause[hidden] {
            display: none;
        }

        .test-fullscreen-pause h2 {
            margin: 0 0 8px;
            color: var(--primary);
        }

        .test-fullscreen-pause p {
            margin: 0 0 18px;
            color: var(--neutral-muted);
        }

        .test-mode.test-fullscreen-paused .progress-container,
        .test-mode.test-fullscreen-paused .quiz-card {
            display: none !important;
        }

        .test-result-export {
            margin: 0 0 24px;
            padding: 18px;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            background: #f7fafb;
        }

        .test-result-export[hidden] {
            display: none;
        }

        .test-result-export h3 {
            margin: 0 0 6px;
            color: var(--primary);
        }

        .test-result-export p {
            color: var(--neutral-muted);
        }

        .test-access {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
            gap: 14px;
            margin: 16px 0 8px;
            max-width: 560px;
        }

        .test-access select,
        .test-access input {
            width: 100%;
            min-height: 48px;
            padding: 10px 14px;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: #fff;
            font: inherit;
            box-sizing: border-box;
        }

        .test-result-intro {
            margin: 0 0 14px;
        }

        .test-result-fields {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
            gap: 14px;
        }

        .test-result-field label {
            display: block;
            margin-bottom: 6px;
            font-weight: 700;
            font-size: 0.92rem;
            color: var(--neutral-dark);
        }

        .test-result-field input {
            width: 100%;
            min-height: 48px;
            padding: 10px 14px;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: #fff;
            font: inherit;
            font-size: 1rem;
            box-sizing: border-box;
        }

        .test-result-field input:focus {
            outline: 3px solid rgba(20, 125, 120, 0.35);
            border-color: var(--primary);
        }

        .test-result-actions {
            display: flex;
            flex-wrap: wrap;
            gap: 10px;
            margin-top: 16px;
        }

        .test-result-actions .btn {
            min-height: 48px;
        }

        .test-result-status:empty {
            display: none;
        }

        .test-result-status {
            margin: 10px 0 0;
            font-weight: 600;
        }

        .test-lockout-card {
            display: flex;
            align-items: flex-start;
            gap: 16px;
            margin: 0 0 24px;
            padding: clamp(20px, 4vw, 32px);
            border: 1px solid #f0c7c4;
            border-radius: var(--radius);
            background: #fff8f7;
            box-shadow: var(--card-shadow);
        }

        .test-lockout-card[hidden] {
            display: none;
        }

        .test-lockout-icon {
            display: grid;
            flex: 0 0 38px;
            width: 38px;
            height: 38px;
            place-items: center;
            border-radius: 50%;
            background: #bd3b36;
            color: #fff;
            font-size: 1.25rem;
            font-weight: 850;
        }

        .test-lockout-card h2 {
            margin: 0 0 6px;
            color: #8c2824;
            font-size: 1.35rem;
        }

        .test-lockout-card p {
            margin: 0 0 18px;
            color: var(--neutral-muted);
        }

        .test-mode .workspace-breadcrumb,
        .test-mode .site-footer,
        .test-mode #btn-overview {
            display: none;
        }

        .test-mode .question-jump {
            width: min(100%, 1040px);
            margin-inline: auto;
        }

        .test-mode .navigator-scroll {
            max-height: none;
            overflow: visible;
        }

        .test-mode .quiz-actions {
            position: sticky;
            bottom: 0;
            z-index: 4;
            justify-content: space-between;
            gap: 10px;
            padding: 12px 0;
            background: linear-gradient(to top, #fff 80%, rgba(255, 255, 255, 0));
        }

        .test-mode .quiz-actions .btn {
            flex: 1 1 0;
            justify-content: center;
        }

        .test-mode .question-title {
            font-size: calc(1.15rem * var(--test-text-scale, 1));
        }

        .test-mode .option-label {
            font-size: calc(1rem * var(--test-text-scale, 1));
        }

        .test-mode .question-nav-btn {
            width: 48px;
            height: 48px;
            font-size: 0.95rem;
        }

        .question-nav-btn.flagged {
            box-shadow: inset 0 0 0 3px #f59e0b;
        }

        .question-nav-btn.flagged::after {
            content: '⚑';
            position: absolute;
            top: -6px;
            right: -4px;
            font-size: 0.75rem;
            color: #b45309;
        }

        .question-nav-btn {
            position: relative;
        }

        .btn-flag[aria-pressed="true"] {
            background: #fef3c7;
            border-color: #f59e0b;
            color: #92400e;
        }

        .test-text-size {
            display: flex;
            gap: 6px;
        }

        .test-text-size button {
            min-width: 44px;
            min-height: 44px;
            border: 1px solid var(--border-color);
            border-radius: 10px;
            background: #fff;
            font-weight: 800;
            cursor: pointer;
        }

        .stat-badge.timer-low {
            background: #fef3c7;
            border-color: #f59e0b;
            color: #92400e;
        }

        .stat-badge.timer-critical {
            background: #fee2e2;
            border-color: #ef4444;
            color: #991b1b;
        }

        .test-review-card[hidden] {
            display: none;
        }

        .test-review-card h3 {
            margin: 18px 0 8px;
            font-size: 1rem;
        }

        .preview-detail > summary {
            display: flex;
            justify-content: space-between;
            gap: 12px;
            cursor: pointer;
            list-style: none;
        }

        .preview-detail-body {
            margin-top: 10px;
            padding-top: 10px;
            border-top: 1px solid var(--border-color);
            font-size: 0.92rem;
        }

        .preview-detail-body p {
            margin: 0 0 8px;
        }

        #resume-chapter-test {
            margin-top: 10px;
        }

        /* Locked exam view: the page never scrolls; only the question card scrolls internally. */
        html:has(body.test-mode),
        body.test-mode {
            overflow: hidden;
            overscroll-behavior: none;
            height: 100%;
        }

        body.test-mode #assessment-ui:not([hidden]) {
            position: fixed;
            inset: 0;
            z-index: 60;
            display: flex;
            flex-direction: column;
            gap: 8px;
            padding: 10px clamp(10px, 3vw, 28px);
            background: var(--bg, #f8fafc);
            overflow: hidden;
        }

        body.test-mode #assessment-ui > * {
            flex: 0 0 auto;
            width: min(100%, 1040px);
            margin-inline: auto;
        }

        body.test-mode #assessment-ui > .quiz-card {
            flex: 1 1 auto;
            min-height: 0;
            overflow-y: auto;
            overscroll-behavior: contain;
            -webkit-overflow-scrolling: touch;
        }

        body.test-mode #assessment-ui > .quiz-card[hidden] {
            display: none;
        }

        .test-mode .question-jump {
            padding: 4px 10px;
        }

        .test-mode .question-jump .navigator-scroll,
        .test-mode .navigator-grid {
            scrollbar-width: none;
        }

        .test-mode .test-session-banner {
            padding: 6px 12px;
            gap: 8px;
        }

        .test-mode .test-session-banner p {
            display: none;
        }

        .test-mode .test-session-banner[data-state="warning"] p,
        .test-mode .test-session-banner[data-state="alert"] p {
            display: block;
            margin: 0;
        }

        #test-timer-display.timer-low {
            color: #b45309;
        }

        #test-timer-display.timer-critical {
            color: #b91c1c;
        }

        .test-mode .progress-container {
            display: none;
        }

        .test-mode .test-text-size button {
            min-width: 40px;
            min-height: 40px;
        }

        .test-mode .navigator-grid {
            display: flex;
            flex-wrap: nowrap;
            gap: 6px;
            overflow-x: auto;
            padding-bottom: 2px;
        }

        .test-mode .question-nav-btn {
            flex: 0 0 auto;
            width: 44px;
            height: 44px;
        }

        .test-mode .quiz-card {
            width: min(100%, 1040px);
            margin-inline: auto;
        }

        .test-mode .option-label {
            min-height: 56px;
            padding: 16px 20px;
        }

        .test-mode .quiz-actions .btn {
            min-height: 52px;
        }

        .test-mode #question-stem:focus {
            outline: 3px solid rgba(20, 125, 120, 0.35);
            outline-offset: 6px;
            border-radius: 4px;
        }

        @media (pointer: coarse) {
            .test-mode .option-label {
                min-height: 64px;
                padding: 18px 22px;
                font-size: 1rem;
                touch-action: manipulation;
            }

            .test-mode .radio-indicator {
                width: 24px;
                height: 24px;
            }

            .test-mode .quiz-actions .btn,
            .test-fullscreen-pause .btn {
                min-height: 56px;
            }
        }

        @media (max-width: 620px) {
            .test-details {
                grid-template-columns: 1fr;
            }

            .test-details li {
                min-height: 0;
            }

            .test-launch-card #start-chapter-test {
                width: 100%;
                justify-content: center;
            }

            .test-session-banner {
                align-items: flex-start;
                padding: 14px;
            }

            .test-launch-card #start-test-without-fullscreen {
                width: 100%;
                justify-content: center;
            }
        }

        .practice-section {
            scroll-margin-top: 84px;
        }

        #start-full-test {
            scroll-margin-top: 84px;
        }

        .bank-hero-actions {
            display: flex;
            align-items: center;
            flex-wrap: wrap;
            gap: 16px;
            margin-top: 24px;
        }

        .bank-hero .btn-primary {
            min-height: 48px;
            padding: 12px 20px;
            background: var(--secondary);
            border-color: var(--secondary);
            color: white;
            box-shadow: none;
        }

        .bank-hero .btn-primary:hover {
            background: #116b67;
            border-color: #116b67;
        }

        .bank-question-total {
            color: #e0e9ed;
            font-size: 0.88rem;
            font-weight: 600;
        }

        #bank-screen h1,
        #bank-screen h2,
        #bank-screen h3,
        #bank-screen h4 {
            font-family: Georgia, "Times New Roman", serif;
        }

        .objective-card:focus-visible,
        .btn:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 3px;
        }

        .chapter4-question img {
            display: block;
            max-width: 100%;
            max-height: 260px;
            margin: 0 auto;
            object-fit: contain;
            border-radius: 8px;
        }

        .overline {
            text-decoration: overline;
        }

        .objective-list {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
            gap: 14px;
        }

        .topic-accordion {
            grid-column: 1 / -1;
            overflow: hidden;
            border: 1px solid var(--border-color);
            border-radius: 14px;
            background: white;
        }

        .topic-accordion summary {
            display: flex;
            align-items: center;
            justify-content: space-between;
            gap: 12px;
            padding: 16px 18px;
            color: var(--primary);
            cursor: pointer;
            font-weight: 750;
            list-style-position: inside;
        }

        .topic-accordion summary:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: -3px;
        }

        .topic-accordion[open] > summary {
            border-bottom: 1px solid var(--border-color);
            background: #f5faf9;
        }

        .topic-accordion-count {
            flex-shrink: 0;
            color: var(--neutral-muted);
            font-size: 0.78rem;
            font-weight: 650;
        }

        .topic-objective-list {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
            gap: 12px;
            padding: 14px;
        }

        .objective-card {
            display: flex;
            flex-direction: column;
            align-items: flex-start;
            gap: 9px;
            padding: 18px;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            background: #fbfcfc;
            color: var(--neutral-dark);
            text-align: left;
            cursor: pointer;
            transition: transform 0.18s ease, border-color 0.18s ease, background 0.18s ease, box-shadow 0.18s ease;
        }

        .objective-card:hover {
            transform: translateY(-2px);
            border-color: #9ab8bd;
            background: #f2f8f7;
            box-shadow: 0 10px 20px -17px rgba(24, 50, 75, 0.6);
        }

        .objective-card strong {
            font-size: 0.98rem;
        }

        .objective-count {
            color: var(--primary);
            font-size: 0.8rem;
            font-weight: 700;
        }

        .navigator-header {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-bottom: 12px;
            font-size: 0.85rem;
            font-weight: 700;
            color: var(--neutral-muted);
        }

        .navigator-scroll {
            max-height: 340px;
            overflow-y: auto;
            padding: 2px 6px 6px 2px;
        }

        .navigator-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(190px, 1fr));
            gap: 14px;
        }

        .objective-nav-section h3 {
            color: var(--neutral-muted);
            font-size: 0.76rem;
            line-height: 1.35;
            margin-bottom: 7px;
        }

        .objective-nav-case {
            padding: 10px 12px;
            border: 1px solid var(--border-color);
            border-radius: 12px;
        }

        .objective-nav-case + .objective-nav-case {
            margin-top: 10px;
        }

        .objective-nav-case h4 {
            color: var(--neutral-muted);
            font-size: 0.72rem;
            line-height: 1.35;
            margin: 0 0 7px;
        }

        .objective-nav-buttons {
            display: flex;
            flex-wrap: wrap;
            gap: 6px;
        }

        .question-nav-btn {
            width: 42px;
            height: 42px;
            border-radius: 10px;
            border: 1px solid var(--border-color);
            background: var(--neutral-light);
            color: var(--neutral-dark);
            font-weight: 700;
            font-size: 0.8rem;
            cursor: pointer;
            transition: all 0.2s ease;
            flex-shrink: 0;
        }

        @media (max-width: 520px) {
            body {
                padding: 16px 12px;
            }

            header {
                padding: 14px 16px;
            }

            .site-header-main {
                align-items: flex-start;
            }

            .brand {
                flex: 1 1 100%;
                gap: 8px;
            }

            .brand-icon {
                width: 64px;
                height: 49px;
            }

            .brand-title .brand-name {
                font-size: 1.05rem;
            }

            .brand-title p {
                gap: 4px;
                font-size: 0.72rem;
            }

            #current-chapter-title,
            #header-meta {
                padding: 2px 6px;
            }

            .site-header-actions {
                width: 100%;
                justify-content: space-between;
            }

            .header-home-link {
                padding: 8px 9px;
                font-size: 0.74rem;
            }

            .site-footer {
                margin: 30px -12px -16px;
                padding: 30px 12px 16px;
            }

            .site-footer-grid {
                grid-template-columns: 1fr;
                gap: 22px;
                padding-bottom: 20px;
            }

            .site-footer-bottom {
                align-items: flex-start;
                flex-direction: column;
            }

            .subject-portal {
                grid-template-columns: 1fr;
            }

            .subject-sidebar {
                padding: 12px;
                border-right: 0;
                border-bottom: 1px solid #243448;
            }

            .subject-track-list {
                grid-template-columns: repeat(2, minmax(0, 1fr));
            }

            .subject-track-button {
                min-height: 41px;
                padding: 7px;
                font-size: 0.7rem;
            }

            .subject-track-glyph {
                width: 22px;
                height: 22px;
            }

            .subject-track-count {
                display: none;
            }

            .subject-sidebar-footer {
                display: none;
            }

            .subject-catalog-content {
                padding: 20px 14px;
            }

            .subject-chapter-grid {
                grid-template-columns: 1fr;
            }

            .bank-card {
                padding: 0 18px 22px;
            }

            .bank-hero {
                margin: 0 -18px 25px;
                padding: 32px 20px;
            }

            .bank-hero.chapter13-hero .bank-hero-layout {
                grid-template-columns: minmax(0, 1fr);
                gap: 24px;
            }

            .chapter13-hero-visual {
                min-height: 205px;
                padding: 16px;
            }

            .chapter13-hero-visual svg {
                width: min(100%, 230px);
            }

            .chapter13-random-quiz {
                grid-template-columns: 1fr;
            }

            .chapter13-random-quiz button {
                width: 100%;
            }

            .learning-outcomes {
                grid-template-columns: 1fr;
                gap: 7px;
            }

            .learning-navigation {
                top: 6px;
                gap: 4px;
                margin: -4px 0 18px;
                padding: 7px;
            }

            .learning-navigation .chapter13-tab-button {
                padding: 7px 8px;
                font-size: 0.76rem;
            }

            .lesson-guide-heading h2 {
                font-size: 1.55rem;
            }

            .lesson-topic-content {
                padding: 12px;
            }

            .chapter13-reference-section {
                padding: 12px;
            }

            .chapter13-guide-card-grid,
            .chapter13-guide-card-grid.two-columns {
                grid-template-columns: 1fr;
            }

            .reference-angle-lab,
            .special-triangle-grid,
            .calculator-pitfalls {
                grid-template-columns: 1fr;
            }

            .reference-side-key {
                gap: 4px;
            }

            .reference-side-key strong {
                font-size: 0.67rem;
            }

            .reference-side-key span {
                font-size: 0.62rem;
            }

            .special-ratio-table {
                font-size: 0.78rem;
            }

            .special-ratio-table th,
            .special-ratio-table td {
                padding: 7px 4px;
            }

            .chapter13-tool-grid,
            .chapter13-prerequisite-grid,
            .triangle-lab-layout,
            .calculator-tip-grid {
                grid-template-columns: 1fr;
            }

            .triangle-side-key {
                gap: 7px 10px;
                font-size: 0.73rem;
            }

            .bank-hero::after {
                right: 12px;
                opacity: 0.6;
            }

            .bank-hero-description {
                max-width: 390px;
                font-size: 0.94rem;
            }

            .bank-hero-actions {
                align-items: flex-start;
                flex-direction: column;
                gap: 10px;
            }

            .objective-list,
            .topic-objective-list {
                grid-template-columns: 1fr;
            }

            .navigator-grid {
                grid-template-columns: 1fr;
            }
        }

        @media (min-width: 521px) and (max-width: 820px) {
            .subject-portal {
                grid-template-columns: 210px minmax(0, 1fr);
            }

            .subject-track-button {
                font-size: 0.72rem;
            }

            .bank-hero.chapter13-hero .bank-hero-layout {
                grid-template-columns: minmax(0, 1.3fr) minmax(210px, 0.8fr);
                gap: 22px;
            }

            .chapter13-hero-visual {
                min-height: 220px;
                padding: 14px;
            }

        }

        @media (min-width: 521px) and (max-width: 1024px) and (pointer: coarse) {
            .test-mode .test-session-banner {
                position: sticky;
                top: 8px;
                z-index: 5;
                box-shadow: 0 4px 14px rgba(24, 50, 75, 0.1);
            }

            .test-mode .diagram-container {
                min-height: 220px;
            }
        }

        @media (min-width: 521px) and (max-width: 700px) {
            .reference-angle-lab {
                grid-template-columns: 1fr;
            }
        }

        @media (prefers-reduced-motion: reduce) {
            *,
            *::before,
            *::after {
                scroll-behavior: auto !important;
                animation-duration: 0.01ms !important;
                transition-duration: 0.01ms !important;
            }
        }

        .question-nav-btn:hover {
            border-color: #9ab8bd;
            background: var(--primary-light);
        }

        .question-nav-btn.active {
            background: var(--primary);
            border-color: var(--primary);
            color: white;
            box-shadow: 0 6px 16px rgba(24, 50, 75, 0.2);
        }

        .question-nav-btn.answered {
            background: var(--success-light);
            border-color: #a7f3d0;
            color: #065f46;
        }

        .question-nav-btn.active.answered {
            background: var(--primary);
            border-color: var(--primary);
            color: white;
        }

        /* Main Quiz Card */
        .quiz-card {
            background: white;
            border-radius: var(--radius);
            padding: 32px;
            box-shadow: var(--card-shadow);
            border: 1px solid var(--border-color);
            margin-bottom: 24px;
            min-width: 0;
        }

        .question-header {
            display: flex;
            justify-content: space-between;
            align-items: flex-start;
            margin-bottom: 20px;
            gap: 16px;
        }

        .question-header > div:first-child {
            flex: 1 1 0;
            min-width: 0;
        }

        .question-title {
            font-size: 1.15rem;
            font-weight: 700;
            color: var(--neutral-dark);
            line-height: 1.4;
            overflow-wrap: anywhere;
        }

        .question-table {
            width: min(100%, 620px);
            border-collapse: collapse;
            margin: 14px 0;
            font-size: 0.95rem;
            table-layout: fixed;
        }

        .question-table th,
        .question-table td {
            border: 1px solid var(--border-color);
            padding: 6px 12px;
            text-align: center;
            white-space: nowrap;
        }

        .question-table th {
            background: var(--primary-light);
            color: var(--neutral-dark);
        }

        .tag-badge {
            background: var(--primary-light);
            color: var(--primary);
            font-size: 0.75rem;
            font-weight: 700;
            padding: 4px 10px;
            border-radius: 6px;
            flex: 0 1 auto;
            max-width: 42%;
            white-space: normal;
            overflow-wrap: anywhere;
            line-height: 1.4;
            text-transform: uppercase;
        }

        /* Interactive Grid Layout */
        .quiz-body {
            display: grid;
            grid-template-columns: 1fr 1fr;
            gap: 28px;
            align-items: center;
        }

        .quiz-body.no-diagram {
            grid-template-columns: 1fr;
        }

        .quiz-body.no-diagram .diagram-container {
            display: none;
        }

        .quiz-body.no-diagram .options-list {
            display: grid;
            grid-template-columns: repeat(2, minmax(0, 1fr));
            gap: 16px;
        }

        @media (max-width: 768px) {
            .chapter13-guide-card-grid.two-columns.objective4-trig-grid,
            .chapter13-guide-card-grid.objective4-pythagorean-grid {
                grid-template-columns: 1fr;
            }

            .quiz-card {
                padding: 24px;
            }

            .question-header {
                flex-direction: column;
                align-items: stretch;
                gap: 10px;
            }

            .question-header > div:first-child {
                width: 100%;
            }

            .tag-badge {
                align-self: flex-start;
                max-width: 100%;
                text-align: left;
            }

            .quiz-body {
                grid-template-columns: 1fr;
            }

            .quiz-body.no-diagram .options-list {
                grid-template-columns: 1fr;
            }
        }

        /* SVG Diagram Box */
        .diagram-container {
            background: #f8fafc;
            border: 1px solid var(--border-color);
            border-radius: 14px;
            padding: 16px;
            display: flex;
            justify-content: center;
            align-items: center;
            min-height: 280px;
            position: relative;
        }

        .line-graph-question {
            width: 100%;
            display: flex;
            justify-content: center;
        }

        .line-graph-question img {
            display: block;
            width: min(100%, 720px);
            height: auto;
        }

        .bar-graph-question {
            width: 100%;
            display: flex;
            justify-content: center;
        }

        .bar-graph-question img {
            display: block;
            width: min(100%, 720px);
            height: auto;
        }

        .pie-chart-question {
            width: 100%;
            display: flex;
            justify-content: center;
        }

        .pie-chart-question img {
            display: block;
            width: min(100%, 420px);
            height: auto;
        }

        .diagram-container svg {
            width: 100%;
            max-width: 300px;
            height: auto;
            max-height: 260px;
        }

        .trig-expression {
            color: var(--neutral-dark);
            font-size: clamp(1.6rem, 5vw, 2.6rem);
            font-weight: 700;
            text-align: center;
            padding: 24px;
        }

        .frac {
            display: inline-flex;
            flex-direction: column;
            align-items: center;
            vertical-align: middle;
            text-align: center;
            margin-left: 4px;
        }

        .frac-num {
            border-bottom: 1.5px solid currentColor;
            padding: 0 6px 2px;
        }

        .frac-den {
            padding: 2px 6px 0;
        }

        /* Options Form */
        .options-list {
            display: flex;
            flex-direction: column;
            gap: 12px;
        }

        .option-item {
            position: relative;
        }

        .option-item input[type="radio"] {
            position: absolute;
            opacity: 0;
            cursor: pointer;
        }

        .option-label {
            display: flex;
            align-items: center;
            justify-content: space-between;
            padding: 14px 18px;
            border: 2px solid var(--border-color);
            border-radius: 12px;
            cursor: pointer;
            transition: all 0.2s ease;
            font-weight: 500;
            font-size: 0.95rem;
            background: white;
        }

        .option-label:hover {
            border-color: #9ab8bd;
            background: #f8fafc;
        }

        .option-item input[type="radio"]:checked + .option-label {
            border-color: var(--primary);
            background: var(--primary-light);
            color: var(--primary);
            font-weight: 600;
        }

        .radio-indicator {
            width: 20px;
            height: 20px;
            border-radius: 50%;
            border: 2px solid #cbd5e1;
            margin-right: 12px;
            display: flex;
            align-items: center;
            justify-content: center;
            transition: all 0.2s ease;
            flex-shrink: 0;
        }

        .option-item input[type="radio"]:checked + .option-label .radio-indicator {
            border-color: var(--primary);
            background: var(--primary);
        }

        .radio-indicator::after {
            content: '';
            width: 8px;
            height: 8px;
            border-radius: 50%;
            background: white;
            display: none;
        }

        .option-item input[type="radio"]:checked + .option-label .radio-indicator::after {
            display: block;
        }

        .option-text {
            flex-grow: 1;
        }

        .option-image {
            display: block;
            max-width: min(100%, 300px);
            max-height: 190px;
            margin-top: 0.35rem;
            object-fit: contain;
        }

        /* Action Buttons */
        .quiz-actions {
            display: flex;
            justify-content: space-between;
            align-items: center;
            margin-top: 24px;
            padding-top: 20px;
            border-top: 1px solid var(--border-color);
        }

        @media (max-width: 520px) {
            .quiz-actions {
                display: grid;
                grid-template-columns: repeat(2, minmax(0, 1fr));
                gap: 10px;
            }

            .quiz-actions .btn {
                min-width: 0;
                justify-content: center;
                padding: 10px 8px;
                font-size: 0.84rem;
                text-align: center;
            }

            .quiz-actions button[onclick="returnToBank()"] {
                grid-column: 1 / -1;
                grid-row: 2;
            }
        }

        .btn {
            padding: 12px 24px;
            border-radius: 10px;
            font-weight: 600;
            font-size: 0.95rem;
            cursor: pointer;
            border: none;
            transition: all 0.2s ease;
            display: flex;
            align-items: center;
            gap: 8px;
            text-decoration: none;
        }

        .btn-secondary {
            background: #e2e8f0;
            color: var(--neutral-dark);
        }

        .btn-secondary:hover:not(:disabled) {
            background: #cbd5e1;
        }

        .btn-primary {
            background: var(--primary);
            color: white;
        }

        .btn-primary:hover:not(:disabled) {
            background: var(--primary-hover);
            box-shadow: 0 4px 12px rgba(24, 50, 75, 0.3);
        }

        .btn-success {
            background: var(--success);
            color: white;
        }

        .btn-success:hover {
            background: #059669;
        }

        .btn:disabled {
            opacity: 0.5;
            cursor: not-allowed;
        }

        /* English-only solution feedback */
        .feedback-box {
            margin-top: 24px;
            padding: 20px;
            border-radius: 14px;
            display: none;
            animation: fadeIn 0.3s ease-in-out;
        }

        .feedback-box.correct {
            background: var(--success-light);
            border: 1px solid #a7f3d0;
            color: #065f46;
        }

        .feedback-box.incorrect {
            background: var(--danger-light);
            border: 1px solid #fecaca;
            color: #991b1b;
        }

        .feedback-header {
            font-weight: 700;
            font-size: 1.05rem;
            margin-bottom: 14px;
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .solution-toggle {
            padding: 8px 12px;
            border: 1px solid currentColor;
            border-radius: 8px;
            background: rgba(255, 255, 255, 0.6);
            color: inherit;
            font: inherit;
            font-size: 0.86rem;
            font-weight: 700;
            cursor: pointer;
        }

        .solution-toggle:hover {
            background: white;
        }

        .solution-toggle:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 3px;
        }

        .question-hint-area {
            margin-top: 14px;
        }

        .hint-toggle {
            padding: 8px 12px;
            border: 1px solid #9ab8bd;
            border-radius: 8px;
            background: #f2f8f7;
            color: var(--primary);
            font: inherit;
            font-size: 0.86rem;
            font-weight: 700;
            cursor: pointer;
        }

        .quiz-calc-toggle { margin-left: 8px; }

        .quiz-calc-panel {
            position: fixed;
            right: 16px;
            bottom: 16px;
            z-index: 900;
            width: min(380px, calc(100vw - 24px));
            max-height: calc(100vh - 32px);
            overflow: auto;
            background: #fff;
            border: 1px solid #9ab8bd;
            border-radius: 12px;
            box-shadow: 0 12px 36px rgba(15, 35, 50, 0.35);
        }

        .quiz-calc-panel[hidden] { display: none; }

        .quiz-calc-bar {
            display: flex;
            align-items: center;
            justify-content: space-between;
            padding: 8px 12px;
            background: #17324a;
            color: #fff;
            font-weight: 700;
            border-radius: 11px 11px 0 0;
        }

        .quiz-calc-panel .quiz-calc-close {
            width: 32px;
            height: 32px;
            padding: 0;
            border: 0;
            border-radius: 6px;
            background: transparent;
            color: #fff;
            font-size: 1.4rem;
            line-height: 1;
            cursor: pointer;
        }

        .quiz-calc-body { padding: 8px; }

        .hint-toggle:hover {
            background: #e5f1ef;
        }

        .hint-toggle:focus-visible {
            outline: 3px solid #c99d4e;
            outline-offset: 3px;
        }

        .hint-panel {
            max-width: 760px;
            margin-top: 10px;
            padding: 12px 14px;
            border-left: 3px solid var(--secondary);
            border-radius: 0 8px 8px 0;
            background: #f2f8f7;
            color: var(--neutral-dark);
            font-size: 0.9rem;
        }

        .question-hint-area[hidden],
        .hint-panel[hidden] {
            display: none;
        }

        .solution-panel {
            margin-top: 12px;
            padding: 16px;
            border: 1px solid rgba(32, 51, 68, 0.12);
            border-radius: 10px;
            background: rgba(255, 255, 255, 0.72);
            color: var(--neutral-dark);
            font-size: 0.9rem;
            line-height: 1.6;
        }

        .solution-panel h3 {
            margin-bottom: 8px;
            color: var(--primary);
            font-size: 1rem;
        }

        .solution-hint {
            margin-bottom: 10px;
        }

        .solution-steps {
            padding-left: 1.35rem;
        }

        .solution-steps li + li {
            margin-top: 6px;
        }

        @media (max-width: 420px) {
            .feedback-box {
                padding: 10px;
            }

            .solution-panel {
                padding: 10px;
            }

            .worked-example-steps {
                padding: 10px 8px;
            }
        }

        .math-render-warning {
            margin-top: 12px;
            padding: 10px 12px;
            border: 1px solid #e6c46f;
            border-radius: 8px;
            background: #fff8e6;
            color: #604a14;
            font-size: 0.9rem;
        }

        /* Results Screen */
        .results-card {
            background: white;
            border-radius: var(--radius);
            padding: 36px;
            box-shadow: var(--card-shadow);
            border: 1px solid var(--border-color);
            display: none;
        }

        .results-header {
            text-align: center;
            margin-bottom: 24px;
        }

        .results-score-circle {
            width: 120px;
            height: 120px;
            border-radius: 50%;
            background: linear-gradient(135deg, var(--primary-light), #dce8ed);
            color: var(--primary);
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            margin: 0 auto 16px auto;
            border: 4px solid white;
            box-shadow: 0 6px 16px rgba(24, 50, 75, 0.15);
        }

        .score-num {
            font-size: 2.2rem;
            font-weight: 800;
            line-height: 1;
        }

        .score-denom {
            font-size: 0.85rem;
            font-weight: 600;
            opacity: 0.8;
        }

        /* Detailed Answers Review List */
        .answers-preview {
            background: #f8fafc;
            border: 1px solid var(--border-color);
            border-radius: 12px;
            padding: 20px;
            margin-bottom: 24px;
            max-height: 280px;
            overflow-y: auto;
        }

        .answers-preview h4 {
            font-size: 0.95rem;
            margin-bottom: 12px;
            color: var(--neutral-dark);
        }

        .preview-item {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 8px 12px;
            background: white;
            border: 1px solid var(--border-color);
            border-radius: 6px;
            margin-bottom: 6px;
            font-size: 0.85rem;
        }

        .preview-item.correct-ans {
            border-left: 4px solid var(--success);
        }

        .preview-item.incorrect-ans {
            border-left: 4px solid var(--danger);
        }

        .action-email-container {
            display: flex;
            justify-content: center;
            margin-top: 20px;
        }

        .email-result-note {
            max-width: 640px;
            margin: 12px auto 0;
            color: var(--neutral-muted);
            font-size: 0.9rem;
            text-align: center;
        }

        .result-email-details {
            max-width: 520px;
            margin: 0 auto 20px;
            display: grid;
            gap: 14px;
        }

        .result-email-details label {
            display: block;
            margin-bottom: 6px;
            color: var(--neutral-dark);
            font-size: 0.9rem;
            font-weight: 600;
        }

        .result-email-details input,
        .result-email-details select {
            width: 100%;
            padding: 10px 12px;
            border: 1px solid var(--border-color);
            border-radius: 8px;
            font: inherit;
        }

        .result-email-details input:focus-visible,
        .result-email-details select:focus-visible {
            outline: 2px solid var(--primary);
            outline-offset: 2px;
        }

        @media (pointer: coarse) {
            .result-email-details input,
            .result-email-details select {
                min-height: 52px;
                padding: 12px 14px;
            }

            .action-email-container {
                flex-wrap: wrap;
                gap: 12px;
            }

            .action-email-container .btn,
            .test-result-export .btn {
                min-height: 52px;
                justify-content: center;
            }
        }

        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(8px); }
            to { opacity: 1; transform: translateY(0); }
        }