/* 中小学生风格色系：明亮、活泼、柔和，以天蓝、柠檬黄、嫩绿、暖橙为主 */
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            background: linear-gradient(145deg, #f9f3e8 0%, #fef9ef 100%);
            font-family: 'Segoe UI', 'PingFang SC', Roboto, 'Helvetica Neue', sans-serif;
            padding: 2rem 1.5rem 3rem;
            min-height: 100vh;
            display: flex;
            flex-direction: column;
            align-items: center;
        }

        /* 主容器 – 像一本打开的练习册 */
        .course-wrapper {
            max-width: 1400px;
            width: 100%;
            background: rgba(255, 255, 255, 0.7);
            backdrop-filter: blur(2px);
            border-radius: 48px 48px 32px 32px;
            padding: 2rem 2rem 2.5rem;
            box-shadow: 0 20px 40px rgba(255, 193, 7, 0.12), 0 8px 24px rgba(0, 150, 136, 0.08);
            border: 2px solid rgba(255, 214, 0, 0.25);
        }

        /* 页眉 – 彩色铅笔风格 */
        .header {
            display: flex;
            flex-wrap: wrap;
            align-items: center;
            justify-content: space-between;
            margin-bottom: 2rem;
            border-bottom: 4px dashed #ffb74d;
            padding-bottom: 1.2rem;
        }

        .title-group {
            display: flex;
            align-items: baseline;
            gap: 0.5rem;
            flex-wrap: wrap;
        }

        .title-group h1 {
            font-size: 2.4rem;
            font-weight: 700;
            color: #2b5f8a;
            letter-spacing: 1px;
            background: linear-gradient(135deg, #f9a825, #ff8a65);
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
            text-shadow: 0 2px 10px rgba(255, 152, 0, 0.2);
        }

        .title-group .sub {
            font-size: 1.1rem;
            font-weight: 500;
            color: #3e7b5e;
            background: #e0f2e9;
            padding: 0.2rem 1rem;
            border-radius: 40px;
            letter-spacing: 0.5px;
            border: 1px solid #a5d6b7;
        }

        .badge {
            background: #ffd54f;
            color: #2d4a3b;
            padding: 0.4rem 1.2rem;
            border-radius: 60px;
            font-weight: 600;
            font-size: 0.9rem;
            box-shadow: 0 4px 8px rgba(255, 193, 7, 0.3);
            border: 1px solid #ffe082;
        }

        .badge i {
            font-style: normal;
            display: inline-block;
            margin-right: 6px;
        }

        /* 目录网格 – 卡片紧凑，色彩明快 */
        .catalog-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
            gap: 1.2rem;
            margin: 1.5rem 0 0.5rem;
        }

        /* 卡片 – 圆润、轻量、彩色描边 */
        .chapter-card {
            background: white;
            border-radius: 28px;
            padding: 1rem 1.2rem 1rem 1.2rem;
            box-shadow: 0 6px 14px rgba(0, 0, 0, 0.02), 0 2px 8px rgba(96, 125, 139, 0.05);
            transition: all 0.2s ease;
            border: 2px solid transparent;
            background-clip: padding-box;
            position: relative;
            display: flex;
            flex-direction: column;
            cursor: pointer;
            text-decoration: none;
            color: inherit;
            min-height: 100px;
            backdrop-filter: blur(4px);
            background: rgba(255, 255, 255, 0.85);
        }

        /* 每个卡片左侧彩色条 – 中小学生彩色笔触 */
        .chapter-card::before {
            content: '';
            position: absolute;
            left: 0;
            top: 12%;
            height: 76%;
            width: 6px;
            border-radius: 12px;
            background: var(--card-stripe, #42a5f5);
            opacity: 0.6;
            transition: 0.2s;
        }

        .chapter-card:hover {
            transform: translateY(-4px) scale(1.01);
            box-shadow: 0 16px 28px rgba(255, 193, 7, 0.15), 0 6px 16px rgba(0, 150, 136, 0.08);
            border-color: #ffe082;
            background: white;
        }

        .chapter-card:hover::before {
            opacity: 1;
            width: 8px;
        }

        /* 卡片内容紧凑 */
        .card-top {
            display: flex;
            align-items: baseline;
            gap: 0.4rem;
            margin-bottom: 0.3rem;
        }

        .chapter-number {
            font-weight: 700;
            font-size: 1.2rem;
            color: #1e3c5a;
            background: #f1f8fe;
            padding: 0 0.4rem 0 0.6rem;
            border-radius: 30px;
            line-height: 1.6;
            letter-spacing: 0.3px;
            display: inline-block;
            border: 1px solid #bbdefb;
        }

        .chapter-title {
            font-weight: 600;
            font-size: 1rem;
            color: #1f3a4b;
            line-height: 1.3;
            display: inline;
            word-break: break-word;
        }

        .card-desc {
            font-size: 0.82rem;
            color: #3d5a6c;
            margin-top: 0.2rem;
            line-height: 1.4;
            display: -webkit-box;
            -webkit-line-clamp: 2;
            -webkit-box-orient: vertical;
            overflow: hidden;
            opacity: 0.85;
            padding-right: 0.2rem;
        }

        /* 不同章节随机彩色条 – 通过js或内联变量，这里用css变量预设，但为了简洁，在html中直接设置style */
        /* 备用 */

        /* 页脚 */
        .footer-note {
            margin-top: 2.5rem;
            text-align: center;
            font-size: 0.9rem;
            color: #5f7d6e;
            border-top: 2px dotted #ffe082;
            padding-top: 1.5rem;
            display: flex;
            justify-content: center;
            gap: 1.2rem;
            flex-wrap: wrap;
        }

        .footer-note span {
            background: #fff3e0;
            padding: 0.2rem 1.2rem;
            border-radius: 30px;
            font-weight: 500;
            color: #3e5a4b;
        }

        .emoji-icon {
            font-size: 1.1rem;
            margin-right: 4px;
        }

        /* 响应式 */
        @media (max-width: 640px) {
            body { padding: 1rem 0.8rem; }
            .course-wrapper { padding: 1.2rem; }
            .title-group h1 { font-size: 1.8rem; }
            .catalog-grid { grid-template-columns: 1fr; }
            .chapter-card { min-height: 80px; }
        }

        /* 链接重置 */
        a.chapter-card {
            text-decoration: none;
            color: inherit;
        }
        a.chapter-card:visited {
            color: inherit;
        }
        a.chapter-card:active {
            transform: scale(0.98);
        }

        /* 彩色条纹变量 */
        .stripe-blue { --card-stripe: #42a5f5; }
        .stripe-green { --card-stripe: #66bb6a; }
        .stripe-orange { --card-stripe: #ffa726; }
        .stripe-pink { --card-stripe: #ec407a; }
        .stripe-purple { --card-stripe: #ab47bc; }
        .stripe-teal { --card-stripe: #26a69a; }
        .stripe-amber { --card-stripe: #ffca28; }
        .stripe-indigo { --card-stripe: #5c6bc0; }
        .stripe-red { --card-stripe: #ef5350; }
        .stripe-lime { --card-stripe: #c0ca33; }
        .stripe-brown { --card-stripe: #8d6e63; }
        .stripe-cyan { --card-stripe: #00bcd4; }