* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
        }
        
        body {
            background: linear-gradient(135deg, #1a2a6c, #b21f1f, #1a2a6c);
            color: #333;
            min-height: 100vh;
            padding-bottom: 60px;
            overflow-x: hidden;
        }
        
        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 20px;
        }
        
        header {
            text-align: center;
            padding: 30px 0;
            background: rgba(255, 255, 255, 0.95);
            border-radius: 15px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.3);
            margin-bottom: 30px;
            animation: fadeInDown 0.8s ease;
        }
        
        @keyframes fadeInDown {
            from { opacity: 0; transform: translateY(-30px); }
            to { opacity: 1; transform: translateY(0); }
        }
        
        header h1 {
            font-size: 2.8rem;
            color: #1a2a6c;
            margin-bottom: 15px;
            text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.1);
        }
        
        header p {
            font-size: 1.2rem;
            color: #555;
            max-width: 800px;
            margin: 0 auto;
        }
        
        /* 导航栏样式 */
        nav {
            background: linear-gradient(to right, #2c3e50, #4a6491);
            border-radius: 50px;
            padding: 0;
            margin: 20px auto 40px;
            max-width: 900px;
            box-shadow: 0 8px 16px rgba(0, 0, 0, 0.3);
            animation: slideIn 0.8s ease;
        }
        
        @keyframes slideIn {
            from { opacity: 0; transform: translateY(-20px); }
            to { opacity: 1; transform: translateY(0); }
        }
        
        nav ul {
            display: flex;
            justify-content: center;
            list-style: none;
        }
        
        nav li {
            flex: 1;
            text-align: center;
        }
        
        nav a {
            display: block;
            padding: 18px 0;
            color: white;
            text-decoration: none;
            font-size: 1.2rem;
            font-weight: 600;
            transition: all 0.3s ease;
            border-radius: 50px;
        }
        
        nav a:hover {
            background: rgba(255, 255, 255, 0.2);
            transform: translateY(-3px);
        }
        
        nav a.active {
            background: linear-gradient(to right, #3498db, #2ecc71);
            box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
        }
        
        nav a i {
            margin-right: 10px;
        }
        
        /* 内容区域样式 */
        .content-section {
            display: none;
            background: rgba(255, 255, 255, 0.95);
            border-radius: 20px;
            padding: 30px;
            box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
            margin-bottom: 30px;
            animation: fadeIn 0.8s ease;
        }
        
        @keyframes fadeIn {
            from { opacity: 0; transform: translateY(20px); }
            to { opacity: 1; transform: translateY(0); }
        }
        
        .content-section.active {
            display: block;
        }
        
        .content-section h2 {
            color: #1a2a6c;
            font-size: 2.2rem;
            margin-bottom: 25px;
            text-align: center;
            border-bottom: 3px solid #3498db;
            padding-bottom: 15px;
        }
        
        .content-section h3 {
            color: #2c3e50;
            font-size: 1.6rem;
            margin: 25px 0 15px;
        }
        
        .content-section p {
            font-size: 1.1rem;
            line-height: 1.8;
            margin-bottom: 20px;
            color: #444;
        }
        
        .content-section ul, .content-section ol {
            margin-left: 30px;
            margin-bottom: 25px;
        }
        
        .content-section li {
            margin-bottom: 12px;
            font-size: 1.1rem;
            line-height: 1.6;
        }
        
        /* 动画教学区域 */
        .animation-container {
            display: flex;
            flex-wrap: wrap;
            gap: 30px;
            margin-top: 20px;
        }
        
        .graph-container {
            flex: 1;
            min-width: 400px;
            background: #f8f9fa;
            border-radius: 15px;
            padding: 20px;
            box-shadow: inset 0 0 10px rgba(0, 0, 0, 0.1);
        }
        
        #graph {
            width: 100%;
            height: 400px;
            background: white;
            border: 2px solid #2c3e50;
            border-radius: 10px;
        }
        
        .controls {
            flex: 1;
            min-width: 300px;
            background: #f8f9fa;
            border-radius: 15px;
            padding: 25px;
            box-shadow: inset 0 0 10px rgba(0, 0, 0, 0.1);
        }
        
        .control-group {
            margin-bottom: 25px;
        }
        
        .control-group label {
            display: block;
            font-size: 1.2rem;
            font-weight: 600;
            color: #2c3e50;
            margin-bottom: 15px;
        }
        
        .slider-container {
            display: flex;
            align-items: center;
            gap: 15px;
        }
        
        .slider-container input[type="range"] {
            flex: 1;
            height: 12px;
            -webkit-appearance: none;
            background: linear-gradient(to right, #3498db, #2ecc71);
            border-radius: 10px;
            outline: none;
        }
        
        .slider-container input[type="range"]::-webkit-slider-thumb {
            -webkit-appearance: none;
            width: 28px;
            height: 28px;
            background: #1a2a6c;
            border-radius: 50%;
            cursor: pointer;
            box-shadow: 0 3px 6px rgba(0, 0, 0, 0.2);
        }
        
        .slider-container .value {
            font-size: 1.3rem;
            font-weight: bold;
            color: #1a2a6c;
            min-width: 50px;
            text-align: center;
        }
        
        #equation {
            text-align: center;
            font-size: 2.2rem;
            font-weight: bold;
            color: #e74c3c;
            margin: 25px 0;
            padding: 15px;
            background: rgba(231, 76, 60, 0.1);
            border-radius: 10px;
        }
        
        .slope-calculation {
            background: #e3f2fd;
            border-left: 5px solid #2196f3;
            padding: 20px;
            border-radius: 0 10px 10px 0;
            margin-top: 25px;
        }
        
        .slope-calculation h3 {
            color: #2196f3;
            margin-top: 0;
        }
        
        /* 练习区域 */
        .exercise {
            background: #e8f5e9;
            border-radius: 10px;
            padding: 20px;
            margin: 25px 0;
            border-left: 5px solid #4caf50;
        }
        
        .exercise h3 {
            color: #2e7d32;
            margin-top: 0;
        }
        
        .options {
            display: flex;
            flex-wrap: wrap;
            gap: 15px;
            margin: 20px 0;
        }
        
        .option {
            flex: 1;
            min-width: 200px;
            background: white;
            border: 2px solid #c8e6c9;
            border-radius: 10px;
            padding: 15px;
            cursor: pointer;
            transition: all 0.3s ease;
            text-align: center;
        }
        
        .option:hover {
            transform: translateY(-5px);
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
            border-color: #4caf50;
        }
        
        .option.selected {
            background: #c8e6c9;
            border-color: #4caf50;
        }
        
        .feedback {
            padding: 15px;
            border-radius: 10px;
            margin-top: 20px;
            font-weight: bold;
            font-size: 1.2rem;
            display: none;
        }
        
        .feedback.correct {
            background: #c8e6c9;
            color: #2e7d32;
            display: block;
        }
        
        .feedback.incorrect {
            background: #ffcdd2;
            color: #c62828;
            display: block;
        }
        
        .exercise-canvas {
            width: 100%;
            height: 250px;
            background: white;
            border: 2px solid #2c3e50;
            border-radius: 10px;
            margin: 20px 0;
        }
        
        .check-btn {
            background: linear-gradient(to right, #3498db, #2ecc71);
            color: white;
            border: none;
            padding: 10px 25px;
            font-size: 1rem;
            border-radius: 50px;
            cursor: pointer;
            transition: all 0.3s ease;
            box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
            margin-top: 10px;
            display: block;
        }
        
        .check-btn:hover {
            transform: translateY(-3px);
            box-shadow: 0 6px 12px rgba(0, 0, 0, 0.2);
        }
        
        .explanation {
            background: #e3f2fd;
            border-radius: 10px;
            padding: 15px;
            margin-top: 15px;
            display: none;
            border-left: 4px solid #2196f3;
        }
        
        /* 页脚样式 */
        footer {
            text-align: center;
            padding: 25px 0;
            color: white;
            font-size: 1.1rem;
            background: rgba(0, 0, 0, 0.4);
            border-radius: 15px;
            margin-top: 30px;
        }
        
        /* 响应式设计 */
        @media (max-width: 768px) {
            nav ul {
                flex-direction: column;
            }
            
            .animation-container {
                flex-direction: column;
            }
            
            .graph-container {
                min-width: 100%;
            }
            
            .option {
                min-width: 100%;
            }
            
            header h1 {
                font-size: 2.2rem;
            }
        }