:root {
                --primary-color: #4a90d9;
                --primary-dark: #3a7bc8;
                --text-color: #333;
                --text-light: #666;
                --bg-color: #f5f7fa;
                --card-bg: #ffffff;
                --border-color: #e1e5eb;
                --shadow: 0 2px 8px rgba(0,0,0,0.08);
                --shadow-hover: 0 4px 16px rgba(0,0,0,0.12);
                --radius: 12px;
                --radius-sm: 8px;
            }

            * {
                box-sizing: border-box;
            }

            body {
                font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Roboto', 'Oxygen', 'Ubuntu', 'Cantarell', sans-serif;
                line-height: 1.7;
                color: var(--text-color);
                background: linear-gradient(135deg, #f5f7fa 0%, #e4e8ec 100%);
                margin: 0;
                padding: 0;
                min-height: 100vh;
            }

            .mobile-nav {
                position: sticky;
                top: 0;
                background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
                padding: 12px 16px;
                z-index: 1000;
                box-shadow: 0 2px 8px rgba(0,0,0,0.15);
            }

            .nav-home {
                color: white;
                text-decoration: none;
                font-weight: 600;
                font-size: 16px;
                display: inline-flex;
                align-items: center;
                gap: 8px;
                padding: 8px 16px;
                background: rgba(255,255,255,0.15);
                border-radius: var(--radius-sm);
                transition: all 0.2s ease;
            }

            .nav-home:hover {
                background: rgba(255,255,255,0.25);
                transform: translateY(-1px);
            }

            .chapter {
                background: var(--card-bg);
                max-width: 900px;
                margin: 24px auto;
                padding: 32px;
                border-radius: var(--radius);
                box-shadow: var(--shadow);
            }

            .chapter-title {
                color: var(--text-color);
                font-size: 28px;
                font-weight: 700;
                margin: 0 0 24px 0;
                padding-bottom: 16px;
                border-bottom: 3px solid var(--primary-color);
                line-height: 1.3;
            }

            .audio-player {
                background: linear-gradient(135deg, #f8f9ff 0%, #f0f4ff 100%);
                padding: 20px;
                border-radius: var(--radius-sm);
                margin: 24px 0;
                border: 1px solid rgba(74, 144, 217, 0.2);
            }

            .audio-title {
                margin: 0 0 16px 0;
                font-size: 16px;
                color: var(--primary-color);
                font-weight: 600;
            }

            .audio-control {
                width: 100%;
                margin: 8px 0;
                border-radius: var(--radius-sm);
            }

            .page {
                margin: 32px 0;
                padding: 24px 0;
                border-bottom: 1px solid var(--border-color);
            }

            .page:last-child {
                border-bottom: none;
            }

            .page-number {
                display: block;
                text-align: center;
                color: var(--text-light);
                font-size: 13px;
                margin-top: 24px;
                font-weight: 500;
                background: var(--bg-color);
                padding: 6px 16px;
                border-radius: 20px;
                width: fit-content;
                margin-left: auto;
                margin-right: auto;
            }

            img {
                max-width: 100% !important;
                height: auto !important;
                display: block;
                margin: 20px auto;
                border-radius: var(--radius-sm);
                box-shadow: 0 2px 8px rgba(0,0,0,0.1);
                object-fit: contain;
            }

            .page {
                overflow-wrap: break-word;
                word-wrap: break-word;
                word-break: break-word;
                overflow-x: hidden;
            }

            table {
                border-collapse: collapse;
                width: 100%;
                margin: 24px 0;
                overflow-x: auto;
                display: block;
            }

            tbody {
                display: table;
                width: 100%;
            }

            td, th {
                border: 1px solid var(--border-color);
                padding: 14px 12px;
                text-align: left;
            }

            th {
                background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
                color: white;
                font-weight: 600;
                text-transform: uppercase;
                font-size: 13px;
                letter-spacing: 0.5px;
            }

            tr:nth-child(even) {
                background-color: #f8f9fa;
            }

            tr:hover {
                background-color: #f0f4ff;
            }

            .meaning-block {
                padding: 20px;
                margin: 24px 0;
                border-left: 4px solid var(--primary-color);
                background: linear-gradient(135deg, #f8f9ff 0%, #f0f4ff 100%);
                border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
            }

            .block-laboratory {
                border-left-color: #10b981;
                background: linear-gradient(135deg, #f0fdf4 0%, #dcfce7 100%);
            }

            .block-memorize {
                border-left-color: #f59e0b;
                background: linear-gradient(135deg, #fffbeb 0%, #fef3c7 100%);
            }

            .block-questions {
                border-left-color: #ef4444;
                background: linear-gradient(135deg, #fef2f2 0%, #fee2e2 100%);
            }

            .meaning-block-header h3 {
                margin: 0 0 12px 0;
                color: var(--primary-color);
                font-size: 18px;
            }

            .block-laboratory .meaning-block-header h3 {
                color: #10b981;
            }

            .block-memorize .meaning-block-header h3 {
                color: #f59e0b;
            }

            .block-questions .meaning-block-header h3 {
                color: #ef4444;
            }

            figure {
                margin: 24px 0;
                text-align: center;
            }

            figcaption {
                font-style: italic;
                color: var(--text-light);
                margin-top: 12px;
                font-size: 14px;
                line-height: 1.5;
            }

            .chapter-navigation {
                margin-top: 32px;
                padding-top: 24px;
                border-top: 1px solid var(--border-color);
                display: flex;
                justify-content: center;
            }

            .nav-btn {
                display: inline-flex;
                align-items: center;
                gap: 8px;
                padding: 12px 24px;
                background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
                color: white;
                text-decoration: none;
                border-radius: var(--radius-sm);
                font-weight: 600;
                transition: all 0.2s ease;
                box-shadow: 0 2px 8px rgba(74, 144, 217, 0.3);
            }

            .nav-btn:hover {
                transform: translateY(-2px);
                box-shadow: 0 4px 16px rgba(74, 144, 217, 0.4);
            }

            .toc {
                list-style: none;
                padding-left: 0;
                margin: 0;
            }

            .toc li {
                margin: 8px 0;
            }

            .toc ul {
                list-style: none;
                padding-left: 20px;
                margin: 8px 0;
            }

            .toc a {
                color: var(--primary-color);
                text-decoration: none;
                padding: 8px 12px;
                display: block;
                border-radius: var(--radius-sm);
                transition: all 0.2s ease;
            }

            .toc a:hover {
                background: #f0f4ff;
                color: var(--primary-dark);
            }

            .toc-number {
                font-weight: 700;
                color: var(--primary-color);
                margin-right: 4px;
            }

            .toc-info {
                background: linear-gradient(135deg, #f8f9ff 0%, #f0f4ff 100%);
                padding: 20px;
                border-radius: var(--radius-sm);
                margin-bottom: 24px;
                border: 1px solid rgba(74, 144, 217, 0.2);
            }

            .toc-info p {
                margin: 8px 0;
                color: var(--text-light);
            }

            .toc-info strong {
                color: var(--text-color);
            }

            ol, ul {
                padding-left: 24px;
            }

            li {
                margin: 8px 0;
            }

            a {
                color: var(--primary-color);
                text-decoration: underline;
                text-underline-offset: 2px;
            }

            a:hover {
                color: var(--primary-dark);
            }

            em, i {
                color: var(--text-light);
                font-style: italic;
            }

            strong, b {
                font-weight: 600;
                color: var(--text-color);
            }

            @media (max-width: 768px) {
                body {
                    font-size: 16px;
                }

                .chapter {
                    margin: 0;
                    border-radius: 0;
                    padding: 20px 16px;
                    box-shadow: none;
                }

                .chapter-title {
                    font-size: 22px;
                    padding-bottom: 12px;
                }

                .mobile-nav {
                    padding: 10px 12px;
                }

                .nav-home {
                    font-size: 15px;
                    padding: 6px 12px;
                }

                .audio-player {
                    padding: 16px;
                    margin: 20px 0;
                }

                .page {
                    margin: 24px 0;
                    padding: 20px 0;
                }

                table {
                    font-size: 14px;
                }

                td, th {
                    padding: 10px 8px;
                }

                .meaning-block {
                    padding: 16px;
                    margin: 20px 0;
                }

                .meaning-block-header h3 {
                    font-size: 16px;
                }

                img {
                    margin: 16px auto;
                }

                .nav-btn {
                    padding: 10px 20px;
                    font-size: 14px;
                }

                .toc ul {
                    padding-left: 16px;
                }

                .toc a {
                    padding: 6px 10px;
                }
            }

            @media (max-width: 480px) {
                .chapter {
                    padding: 16px 12px;
                }

                .chapter-title {
                    font-size: 20px;
                }

                .page-number {
                    font-size: 12px;
                    padding: 4px 12px;
                }

                figure {
                    margin: 16px 0;
                }

                figcaption {
                    font-size: 13px;
                }
            }

            @media (prefers-color-scheme: dark) {
                :root {
                    --text-color: #e4e4e4;
                    --text-light: #a0a0a0;
                    --bg-color: #1a1a2e;
                    --card-bg: #16213e;
                    --border-color: #2a2a4a;
                    --shadow: 0 2px 8px rgba(0,0,0,0.3);
                }

                body {
                    background: linear-gradient(135deg, #0f0f23 0%, #1a1a2e 100%);
                }

                .audio-player {
                    background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
                    border-color: rgba(74, 144, 217, 0.3);
                }

                .meaning-block {
                    background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
                }

                .block-laboratory {
                    background: linear-gradient(135deg, #064e3b 0%, #065f46 100%);
                }

                .block-memorize {
                    background: linear-gradient(135deg, #78350f 0%, #92400e 100%);
                }

                .block-questions {
                    background: linear-gradient(135deg, #7f1d1d 0%, #991b1b 100%);
                }

                tr:nth-child(even) {
                    background-color: #1a1a2e;
                }

                tr:hover {
                    background-color: #2a2a4a;
                }

                .toc-info {
                    background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
                }
            }