:root {
            --primary-color: #2c5282;
            --primary-hover: #1a365d;
            --secondary-color: #3182ce;
            --accent-color: #e53e3e;
            --success-color: #38a169;
            --warning-color: #dd6b20;
            --info-color: #3182ce;
            --light-bg: #f7fafc;
            --bg-white: #ffffff;
            --border-color: #e2e8f0;
            --text-dark: #2d3748;
            --text-medium: #4a5568;
            --text-light: #718096;
            --text-muted: #a0aec0;
            --shadow: 0 4px 6px rgba(0,0,0,0.05), 0 1px 3px rgba(0,0,0,0.1);
            --shadow-lg: 0 10px 15px rgba(0,0,0,0.1), 0 4px 6px rgba(0,0,0,0.05);
            --radius: 8px;
            --radius-lg: 12px;
        }

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

        body {
            font-family: 'PingFang SC', 'Microsoft YaHei', Arial, sans-serif;
            line-height: 1.65;
            color: var(--text-dark);
            background-color: var(--light-bg);
            display: flex;
            min-height: 100vh;
            overflow-x: hidden;
        }

        /* 左侧导航栏 */
        .sidebar-left {
            width: 260px;
            background-color: var(--bg-white);
            border-right: 1px solid var(--border-color);
            display: flex;
            flex-direction: column;
            position: fixed;
            height: 100vh;
            overflow-y: auto;
            z-index: 10;
            box-shadow: 0 0 10px rgba(0,0,0,0.05);
            transition: transform 0.3s ease;
        }

        .logo-area {
            padding: 24px 20px;
            border-bottom: 1px solid var(--border-color);
            background-color: var(--bg-white);
        }

        .logo {
            font-size: 1.5rem;
            font-weight: 700;
            color: var(--primary-color);
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .logo i {
            color: var(--secondary-color);
            font-size: 1.6rem;
        }

        .nav-tree {
            flex: 1;
            padding: 16px 0;
            overflow-y: auto;
        }

        .nav-section {
            margin-bottom: 24px;
        }

        .nav-section-title {
            font-weight: 600;
            color: var(--primary-color);
            padding: 8px 20px;
            font-size: 0.85rem;
            text-transform: uppercase;
            letter-spacing: 0.5px;
            opacity: 0.8;
        }

        .nav-item {
            padding: 12px 20px 12px 30px;
            display: flex;
            align-items: center;
            cursor: pointer;
            transition: all 0.2s ease;
            border-left: 3px solid transparent;
            position: relative;
        }

        .nav-item:hover {
            background-color: rgba(49, 130, 206, 0.05);
            padding-left: 32px;
        }

        .nav-item.active {
            background-color: rgba(49, 130, 206, 0.1);
            border-left-color: var(--secondary-color);
            font-weight: 600;
            color: var(--primary-color);
        }

        .nav-section:nth-child(1) .nav-item.active {
            border-left-color: var(--secondary-color);
        }

        .nav-section:nth-child(2) .nav-item.active {
            border-left-color: var(--success-color);
        }

        .nav-section:nth-child(3) .nav-item.active {
            border-left-color: var(--warning-color);
        }

        .nav-section:nth-child(4) .nav-item.active {
            border-left-color: var(--accent-color);
        }

        .nav-section:nth-child(5) .nav-item.active {
            border-left-color: var(--info-color);
        }

        .nav-item.completed {
            color: var(--text-light);
        }

        .nav-item.completed::after {
            content: '✓';
            position: absolute;
            right: 20px;
            color: #48bb78;
            font-size: 0.9rem;
        }

        .nav-item i {
            margin-right: 12px;
            font-size: 0.95rem;
            width: 18px;
            text-align: center;
            color: var(--text-medium);
        }

        .nav-item.active i {
            color: var(--secondary-color);
        }

        /* 中央主内容区 */
        .main-content {
            flex: 1;
            margin-left: 260px;
            margin-right: 320px;
            padding: 40px 60px;
            max-width: 900px;
            background-color: var(--bg-white);
            min-height: 100vh;
        }

        .content-header {
            margin-bottom: 48px;
            padding-bottom: 24px;
            border-bottom: 2px solid var(--border-color);
        }

        .chapter-meta {
            display: flex;
            align-items: center;
            margin-bottom: 16px;
            color: var(--text-light);
            font-size: 0.9rem;
        }

        .chapter-number {
            background-color: var(--secondary-color);
            color: white;
            padding: 6px 16px;
            border-radius: 24px;
            font-size: 0.85rem;
            font-weight: 500;
            margin-right: 12px;
        }

        h1 {
            font-size: 2.5rem;
            font-weight: 700;
            color: var(--primary-color);
            margin-bottom: 24px;
            line-height: 1.25;
        }

        .chapter-description {
            font-size: 1.15rem;
            color: var(--text-light);
            line-height: 1.7;
            max-width: 800px;
        }

        /* 内容块通用样式 */
        .content-block {
            margin-bottom: 50px;
        }

        .content-block h2 {
            font-size: 1.7rem;
            margin-bottom: 20px;
            color: var(--text-dark);
            padding-bottom: 10px;
            border-bottom: 3px solid var(--secondary-color);
            font-weight: 600;
        }

        .content-block h3 {
            font-size: 1.3rem;
            margin: 28px 0 16px;
            color: var(--text-dark);
            font-weight: 600;
            display: flex;
            align-items: center;
        }

        .content-block h3::before {
            content: '';
            display: inline-block;
            width: 4px;
            height: 20px;
            background-color: var(--secondary-color);
            margin-right: 10px;
            border-radius: 2px;
        }

        /* 核心规则块 */
        .core-rule {
            background-color: #ebf8ff;
            border-left: 4px solid var(--secondary-color);
            padding: 24px;
            border-radius: 0 var(--radius) var(--radius) 0;
            margin: 28px 0;
            box-shadow: 0 2px 4px rgba(0,0,0,0.05);
        }

        .core-rule:nth-child(odd) {
            background-color: #ebf8ff;
            border-left-color: var(--secondary-color);
        }

        .core-rule:nth-child(even) {
            background-color: #f0fff4;
            border-left-color: var(--success-color);
        }

        .core-rule .content {
            font-size: 1.15rem;
            line-height: 1.6;
            color: var(--text-dark);
            font-weight: 500;
        }

        /* 示例块 */
        .example-block {
            background-color: #f8fafc;
            border: 1px solid var(--border-color);
            border-radius: var(--radius);
            padding: 24px;
            margin: 24px 0;
            position: relative;
            box-shadow: 0 1px 3px rgba(0,0,0,0.05);
        }

        .example-block:nth-child(odd) {
            background-color: #f8fafc;
        }

        .example-block:nth-child(even) {
            background-color: #fefdff;
        }

        .example-block .label {
            position: absolute;
            top: -12px;
            left: 20px;
            background-color: var(--secondary-color);
            color: white;
            padding: 6px 16px;
            border-radius: 6px;
            font-size: 0.85rem;
            font-weight: 600;
        }

        .example-block:nth-child(3n+1) .label {
            background-color: var(--secondary-color);
        }

        .example-block:nth-child(3n+2) .label {
            background-color: var(--success-color);
        }

        .example-block:nth-child(3n+3) .label {
            background-color: var(--warning-color);
        }

        .example-original {
            font-size: 1.3rem;
            margin-bottom: 12px;
            font-weight: 500;
            line-height: 1.5;
            color: var(--text-dark);
        }

        .example-analysis {
            font-family: 'Courier New', monospace;
            background-color: #f1f5f9;
            padding: 12px 16px;
            border-radius: 6px;
            margin: 12px 0;
            font-size: 0.95rem;
            color: var(--text-dark);
            overflow-x: auto;
            border-left: 3px solid var(--secondary-color);
        }

        .example-translation {
            font-style: italic;
            color: var(--text-light);
            padding: 12px 16px;
            border-left: 3px solid var(--secondary-color);
            margin-top: 12px;
            background-color: #f1f5f9;
            border-radius: 0 6px 6px 0;
        }

        /* 对话块 */
        .dialogue-block {
            background-color: #edf2fb;
            border: 1px solid #dbeafe;
            border-radius: var(--radius);
            padding: 24px;
            margin: 24px 0;
            position: relative;
        }

        .dialogue-block .label {
            position: absolute;
            top: -12px;
            left: 20px;
            background-color: var(--secondary-color);
            color: white;
            padding: 6px 16px;
            border-radius: 6px;
            font-size: 0.85rem;
            font-weight: 600;
        }

        .dialogue-line {
            margin-bottom: 18px;
        }

        .dialogue-line:last-child {
            margin-bottom: 0;
        }

        .dialogue-speaker {
            font-weight: 600;
            color: var(--primary-color);
            margin-bottom: 6px;
            font-size: 1rem;
        }

        /* 注意/比较/扩展块 */
        .note-block {
            background-color: #fffbeb;
            border-left: 4px solid #ed8936;
            padding: 20px;
            margin: 24px 0;
            border-radius: 0 var(--radius) var(--radius) 0;
            box-shadow: 0 1px 3px rgba(0,0,0,0.05);
        }

        .note-block .label {
            font-weight: 700;
            color: #c05621;
            margin-bottom: 10px;
            display: flex;
            align-items: center;
            font-size: 1rem;
        }

        .note-block .label i {
            margin-right: 8px;
            color: #ed8936;
        }

        .warning-block {
            background-color: #fef2f2;
            border-left: 4px solid var(--accent-color);
            padding: 20px;
            margin: 24px 0;
            border-radius: 0 var(--radius) var(--radius) 0;
            box-shadow: 0 1px 3px rgba(0,0,0,0.05);
        }

        .warning-block .label {
            font-weight: 700;
            color: var(--accent-color);
            margin-bottom: 10px;
            display: flex;
            align-items: center;
            font-size: 1rem;
        }

        .warning-block .label i {
            margin-right: 8px;
        }

        /* 文本块 */
        .text-block {
            background-color: #f1f5f9;
            border: 1px solid var(--border-color);
            border-radius: var(--radius);
            padding: 24px;
            margin: 24px 0;
            position: relative;
        }

        .text-block .label {
            position: absolute;
            top: -12px;
            left: 20px;
            background-color: var(--secondary-color);
            color: white;
            padding: 6px 16px;
            border-radius: 6px;
            font-size: 0.85rem;
            font-weight: 600;
        }

        /* 右侧词汇栏 */
        .sidebar-right {
            width: 320px;
            background-color: var(--bg-white);
            border-left: 1px solid var(--border-color);
            padding: 32px 24px;
            position: fixed;
            right: 0;
            height: 100vh;
            overflow-y: auto;
            z-index: 10;
            box-shadow: -2px 0 10px rgba(0,0,0,0.05);
        }

        .vocabulary-section {
            margin-bottom: 48px;
        }

        .vocabulary-title {
            font-size: 1.1rem;
            font-weight: 600;
            color: var(--primary-color);
            margin-bottom: 20px;
            padding-bottom: 10px;
            border-bottom: 2px solid var(--border-color);
            display: flex;
            align-items: center;
        }

        .vocabulary-title i {
            margin-right: 10px;
            font-size: 1.2rem;
        }

        .vocabulary-section:nth-child(1) .vocabulary-title {
            color: var(--secondary-color);
            border-bottom-color: var(--secondary-color);
        }

        .vocabulary-section:nth-child(1) .vocabulary-title i {
            color: var(--secondary-color);
        }

        .vocabulary-section:nth-child(2) .vocabulary-title {
            color: var(--success-color);
            border-bottom-color: var(--success-color);
        }

        .vocabulary-section:nth-child(2) .vocabulary-title i {
            color: var(--success-color);
        }

        .vocabulary-section:nth-child(3) .vocabulary-title {
            color: var(--warning-color);
            border-bottom-color: var(--warning-color);
        }

        .vocabulary-section:nth-child(3) .vocabulary-title i {
            color: var(--warning-color);
        }

        .vocabulary-section:nth-child(4) .vocabulary-title {
            color: var(--accent-color);
            border-bottom-color: var(--accent-color);
        }

        .vocabulary-section:nth-child(4) .vocabulary-title i {
            color: var(--accent-color);
        }

        .vocabulary-item {
            background-color: #f8fafc;
            border: 1px solid var(--border-color);
            border-radius: var(--radius);
            padding: 16px;
            margin-bottom: 14px;
            transition: all 0.2s ease;
            cursor: pointer;
        }

        .vocabulary-section:nth-child(1) .vocabulary-item {
            background-color: #ebf8ff;
            border-color: #bee3f8;
        }

        .vocabulary-section:nth-child(1) .vocabulary-item:hover {
            background-color: #bee3f8;
        }

        .vocabulary-section:nth-child(2) .vocabulary-item {
            background-color: #f0fff4;
            border-color: #c6f6d5;
        }

        .vocabulary-section:nth-child(2) .vocabulary-item:hover {
            background-color: #c6f6d5;
        }

        .vocabulary-section:nth-child(3) .vocabulary-item {
            background-color: #fffaf0;
            border-color: #fed7aa;
        }

        .vocabulary-section:nth-child(3) .vocabulary-item:hover {
            background-color: #fed7aa;
        }

        .vocabulary-section:nth-child(4) .vocabulary-item {
            background-color: #fff5f5;
            border-color: #fed7d7;
        }

        .vocabulary-section:nth-child(4) .vocabulary-item:hover {
            background-color: #fed7d7;
        }

        .vocabulary-item:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 6px rgba(0,0,0,0.05);
        }

        .vocabulary-word {
            font-size: 1.1rem;
            font-weight: 600;
            color: var(--primary-color);
            margin-bottom: 6px;
            display: flex;
            align-items: center;
            justify-content: space-between;
        }

        .vocabulary-pronunciation {
            font-size: 0.9rem;
            color: var(--text-light);
            margin-bottom: 8px;
            font-family: 'Courier New', monospace;
        }

        .vocabulary-meaning {
            font-size: 0.95rem;
            color: var(--text-medium);
            line-height: 1.5;
        }

        .vocabulary-category {
            display: inline-block;
            background-color: var(--secondary-color);
            color: white;
            padding: 2px 8px;
            border-radius: 12px;
            font-size: 0.75rem;
            margin-top: 8px;
        }

        /* 菜单按钮 */
        .menu-toggle {
            position: fixed;
            top: 15px;
            left: 15px;
            background-color: var(--primary-color);
            color: white;
            width: 44px;
            height: 44px;
            border-radius: 50%;
            display: flex;
            align-items: center;
            justify-content: center;
            cursor: pointer;
            box-shadow: 0 2px 8px rgba(0,0,0,0.2);
            z-index: 100;
            display: none;
        }

        .menu-toggle.right {
            left: auto;
            right: 15px;
            background-color: var(--secondary-color);
        }

        .menu-toggle i {
            font-size: 1.2rem;
        }

        /* 响应式设计 */
        @media (max-width: 1200px) {
            .sidebar-right {
                width: 280px;
                padding: 24px 18px;
            }
            
            .main-content {
                margin-right: 280px;
                padding: 36px 40px;
            }
        }

        @media (max-width: 992px) {
            .menu-toggle {
                display: flex;
            }
            
            .sidebar-left {
                transform: translateX(-100%);
                transition: transform 0.3s ease;
            }
            
            .sidebar-left.active {
                transform: translateX(0);
                box-shadow: 2px 0 10px rgba(0,0,0,0.1);
            }
            
            .sidebar-right {
                transform: translateX(100%);
                transition: transform 0.3s ease;
            }
            
            .sidebar-right.active {
                transform: translateX(0);
                box-shadow: -2px 0 10px rgba(0,0,0,0.1);
            }
            
            .main-content {
                margin-left: 0;
                margin-right: 0;
                padding: 30px 20px;
                padding-top: 80px;
            }
        }

        @media (max-width: 768px) {
            .main-content {
                padding: 24px 16px;
            }
            
            h1 {
                font-size: 2rem;
            }
            
            .content-block h2 {
                font-size: 1.5rem;
            }
            
            .content-block h3 {
                font-size: 1.2rem;
            }
        }

        /* 导航按钮 */
        .nav-buttons {
            display: flex;
            justify-content: space-between;
            margin-top: 60px;
            padding-top: 24px;
            border-top: 2px solid var(--border-color);
        }

        .nav-button {
            display: inline-flex;
            align-items: center;
            padding: 14px 24px;
            background-color: var(--primary-color);
            color: white;
            text-decoration: none;
            border-radius: var(--radius);
            font-weight: 500;
            transition: all 0.2s ease;
            box-shadow: 0 2px 4px rgba(0,0,0,0.1);
        }

        .nav-button.prev {
            background-color: var(--secondary-color);
        }

        .nav-button.prev:hover {
            background-color: var(--primary-hover);
        }

        .nav-button.next {
            background-color: var(--success-color);
        }

        .nav-button.next:hover {
            background-color: #2f855a;
        }

        .nav-button:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 8px rgba(0,0,0,0.15);
        }

        .nav-button.prev i {
            margin-right: 10px;
        }

        .nav-button.next i {
            margin-left: 10px;
        }

        .nav-button.next {
            margin-left: auto;
        }

        .nav-button:disabled {
            background-color: var(--text-muted);
            cursor: not-allowed;
            transform: none;
            box-shadow: none;
        }

        /* 语法高亮 */
        .grammar-point {
            background-color: #e6ffed;
            padding: 3px 8px;
            border-radius: 6px;
            font-weight: 500;
            color: #22543d;
            border: 1px solid #c6f6d5;
        }

        .structure {
            font-family: 'Courier New', monospace;
            background-color: #f1f5f9;
            padding: 18px 20px;
            border-radius: var(--radius);
            margin: 18px 0;
            overflow-x: auto;
            font-size: 0.95rem;
            color: var(--text-dark);
            border-left: 4px solid var(--secondary-color);
        }

        /* 表格样式 */
        table {
            width: 100%;
            border-collapse: collapse;
            margin: 20px 0;
            background-color: var(--bg-white);
            border-radius: var(--radius);
            overflow: hidden;
            box-shadow: 0 1px 3px rgba(0,0,0,0.05);
        }

        table th {
            background-color: var(--primary-color);
            color: white;
            padding: 12px 16px;
            text-align: left;
            font-weight: 600;
            font-size: 0.95rem;
        }

        table td {
            padding: 10px 16px;
            border-bottom: 1px solid var(--border-color);
            vertical-align: top;
        }

        table tr:last-child td {
            border-bottom: none;
        }

        table tr:nth-child(even) {
            background-color: #f8fafc;
        }

        table tr:hover {
            background-color: #ebf8ff;
        }

        /* 响应式表格 */
        @media (max-width: 768px) {
            table {
                display: block;
                overflow-x: auto;
            }
        }