:root {
            /* 蓝色、白色、灰色调色板 */
            --primary-blue: #1890ff;
            --deep-blue: #096dd9;
            --soft-blue: #e6f7ff;
            --bg-gray: #f8fafc;
            --border-gray: #e2e8f0;
            --text-dark: #1e293b;
            --text-muted: #64748b;
            --white: #ffffff;
            
            /* 阴影与圆角 */
            --radius-lg: 16px;
            --radius-md: 12px;
            --shadow-flat: 0 4px 6px -1px rgba(0, 0, 0, 0.05), 0 2px 4px -1px rgba(0, 0, 0, 0.03);
            --shadow-hover: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
            --transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
        }

        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            -webkit-tap-highlight-color: transparent;
        }

        body {
            font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
            background-color: var(--bg-gray);
            color: var(--text-dark);
            line-height: 1.6;
        }

        /* 玻璃拟态导航栏 */
        header {
            position: sticky;
            top: 0;
            z-index: 1000;
            background: rgba(255, 255, 255, 0.85);
            backdrop-filter: blur(12px);
            -webkit-backdrop-filter: blur(12px);
            border-bottom: 1px solid var(--border-gray);
        }

        .nav-container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 0 24px;
            height: 64px;
            display: flex;
            justify-content: space-between;
            align-items: center;
        }

        .logo {
            font-size: 1.25rem;
            font-weight: 800;
            color: var(--primary-blue);
            text-decoration: none;
            display: flex;
            align-items: center;
            gap: 10px;
        }

        .nav-menu {
            display: flex;
            gap: 24px;
        }

        .nav-menu a {
            text-decoration: none;
            color: var(--text-muted);
            font-size: 0.9rem;
            font-weight: 500;
            transition: var(--transition);
        }

        .nav-menu a:hover {
            color: var(--primary-blue);
        }

        /* 极简 Hero 区域 */
        .hero-section {
            padding: 60px 24px 40px;
            text-align: center;
            max-width: 800px;
            margin: 0 auto;
        }

        .hero-section h1 {
            font-size: 2.5rem;
            font-weight: 800;
            color: var(--text-dark);
            margin-bottom: 16px;
            letter-spacing: -0.025em;
        }

        .hero-section p {
            color: var(--text-muted);
            font-size: 1.1rem;
        }

        /* 核心列表容器 */
        .container {
            max-width: 1200px;
            margin: 0 auto;
            padding: 20px 24px 80px;
        }

        .grid-layout {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
            gap: 24px;
        }

        /* 扁平化卡片设计 */
        .exercise-card {
            background: var(--white);
            border: 1px solid var(--border-gray);
            border-radius: var(--radius-lg);
            padding: 24px;
            position: relative;
            display: flex;
            flex-direction: column;
            justify-content: space-between;
            transition: var(--transition);
            box-shadow: var(--shadow-flat);
        }

        .exercise-card:hover {
            transform: translateY(-8px);
            box-shadow: var(--shadow-hover);
            border-color: var(--primary-blue);
        }

        .card-header {
            display: flex;
            align-items: flex-start;
            gap: 16px;
            margin-bottom: 24px;
        }

        .index-box {
            width: 48px;
            height: 48px;
            background: var(--soft-blue);
            color: var(--primary-blue);
            border-radius: var(--radius-md);
            display: flex;
            align-items: center;
            justify-content: center;
            font-weight: 700;
            font-size: 1.1rem;
            flex-shrink: 0;
            transition: var(--transition);
        }

        .exercise-card:hover .index-box {
            background: var(--primary-blue);
            color: var(--white);
        }

        .title-area h3 {
            font-size: 1.1rem;
            font-weight: 600;
            color: var(--text-dark);
            line-height: 1.5;
        }

        /* 卡片底部操作 */
        .card-footer {
            display: flex;
            align-items: center;
            justify-content: space-between;
            padding-top: 20px;
            border-top: 1px solid var(--bg-gray);
        }

        .start-btn {
            display: inline-flex;
            align-items: center;
            gap: 8px;
            background: var(--primary-blue);
            color: var(--white);
            text-decoration: none;
            padding: 10px 24px;
            border-radius: 50px;
            font-size: 0.9rem;
            font-weight: 600;
            transition: var(--transition);
        }

        .start-btn:hover {
            background: var(--deep-blue);
            box-shadow: 0 10px 15px -3px rgba(24, 144, 255, 0.3);
        }

        /* 响应式调整 */
        @media (max-width: 768px) {
            .nav-menu { display: none; }
            .hero-section h1 { font-size: 1.8rem; }
            .grid-layout { grid-template-columns: 1fr; }
            .exercise-card { padding: 20px; }
        }

        /* 备案信息页脚 */
        footer {
            background: var(--white);
            border-top: 1px solid var(--border-gray);
            padding: 40px 24px;
            text-align: center;
        }

        .footer-info {
            font-size: 0.85rem;
            color: var(--text-muted);
            max-width: 600px;
            margin: 0 auto;
        }

        .beian-link {
            color: var(--text-muted);
            text-decoration: none;
            margin: 0 8px;
            transition: color 0.2s;
        }

        .beian-link:hover {
            color: var(--primary-blue);
        }

        .beian-item {
            margin-top: 8px;
            display: flex;
            justify-content: center;
            align-items: center;
            gap: 5px;
            flex-wrap: wrap;
        }