* {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
            font-family: 'Segoe UI', 'PingFang SC', Roboto, 'Helvetica Neue', sans-serif;
        }

        body {
            background: linear-gradient(145deg, #f9fcfd 0%, #e6f4fa 100%);
            min-height: 100vh;
            padding: 2rem 1.5rem 1rem;
            display: flex;
            flex-direction: column;
            align-items: center;
        }

        .container {
            max-width: 1400px;
            width: 100%;
            background: rgba(255, 255, 255, 0.70);
            backdrop-filter: blur(2px);
            border-radius: 48px 48px 32px 32px;
            padding: 2rem 2rem 1.5rem;
            box-shadow: 0 20px 40px rgba(0, 30, 50, 0.08), 0 8px 20px rgba(0, 0, 0, 0.02);
            border: 1px solid rgba(255, 255, 255, 0.6);
        }

        /* 标题区 — 童趣但不失专业 */
        .header-title {
            display: flex;
            flex-wrap: wrap;
            align-items: baseline;
            justify-content: space-between;
            margin-bottom: 2rem;
            border-bottom: 3px dashed #b0d9e8;
            padding-bottom: 0.75rem;
        }

        .header-title h1 {
            font-size: 2.4rem;
            font-weight: 700;
            background: linear-gradient(135deg, #0077b6, #00b4d8);
            -webkit-background-clip: text;
            -webkit-text-fill-color: transparent;
            background-clip: text;
            letter-spacing: -0.3px;
            display: inline-flex;
            align-items: center;
            gap: 8px;
        }

        .header-title h1::before {
            content: "🧠";
            font-size: 2.6rem;
            background: none;
            -webkit-text-fill-color: initial;
        }

        .header-title .sub {
            font-size: 1rem;
            background: #ffd166;
            padding: 0.3rem 1.2rem;
            border-radius: 40px;
            font-weight: 600;
            color: #1f3a4b;
            box-shadow: 0 4px 8px rgba(255, 209, 102, 0.3);
            display: inline-block;
        }

        /* 课程统计小标签 */
        .stats-badge {
            display: flex;
            gap: 1rem;
            flex-wrap: wrap;
            margin-bottom: 1.8rem;
        }

        .badge-item {
            background: white;
            padding: 0.3rem 1.2rem;
            border-radius: 30px;
            font-size: 0.9rem;
            font-weight: 500;
            color: #1e4a5f;
            box-shadow: 0 2px 6px rgba(0, 128, 128, 0.08);
            border: 1px solid #cae4f0;
        }

        .badge-item span {
            font-weight: 700;
            background: #00b4d8;
            color: white;
            padding: 0 8px;
            border-radius: 20px;
            margin-left: 4px;
        }

        /* 卡片网格 — 紧凑且清晰 */
        .course-grid {
            display: grid;
            grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
            gap: 1.2rem;
            margin: 1.5rem 0 1rem;
        }

        /* 卡片设计：圆润、柔和阴影、彩色小点缀 */
        .card {
            background: white;
            border-radius: 28px;
            padding: 1.2rem 1.2rem 1rem 1.2rem;
            box-shadow: 0 6px 14px rgba(0, 60, 80, 0.06);
            transition: all 0.2s ease;
            border: 1px solid rgba(200, 225, 240, 0.5);
            display: flex;
            flex-direction: column;
            height: 100%;
            backdrop-filter: blur(2px);
            position: relative;
        }

        .card:hover {
            transform: translateY(-4px);
            box-shadow: 0 16px 28px rgba(0, 100, 130, 0.12);
            border-color: #7fc8e0;
        }

        /* 章节编号 + 标题行 */
        .card-header {
            display: flex;
            align-items: baseline;
            gap: 8px;
            margin-bottom: 0.5rem;
            flex-wrap: wrap;
        }

        .chapter-num {
            background: #f2c94c;
            color: #1f3a4b;
            font-weight: 700;
            font-size: 0.8rem;
            padding: 0.1rem 0.8rem;
            border-radius: 40px;
            letter-spacing: 0.3px;
            display: inline-block;
            box-shadow: 0 2px 4px rgba(242, 201, 76, 0.2);
            flex-shrink: 0;
        }

        .card-title {
            font-weight: 700;
            font-size: 1.2rem;
            color: #0a2f44;
            line-height: 1.3;
            letter-spacing: -0.2px;
        }

        .card-title a {
            text-decoration: none;
            color: inherit;
            transition: color 0.1s;
        }

        .card-title a:hover {
            color: #0077b6;
            text-decoration: underline;
            text-underline-offset: 4px;
            text-decoration-color: #90d5ed;
        }

        /* 知识点列表 — 紧凑、小圆点 */
        .topic-list {
            display: flex;
            flex-wrap: wrap;
            gap: 0.3rem 0.6rem;
            margin-top: 0.4rem;
            padding-top: 0.4rem;
            border-top: 1px solid #e3f0f7;
        }

        .topic-item {
            background: #eef7fb;
            padding: 0.15rem 0.7rem;
            border-radius: 30px;
            font-size: 0.75rem;
            color: #1f5b74;
            font-weight: 500;
            letter-spacing: 0.2px;
            border: 1px solid #d2e9f2;
            white-space: nowrap;
        }

        .topic-item::before {
            content: "•";
            color: #f2a900;
            font-weight: bold;
            margin-right: 3px;
        }

        /* 页脚 */
        .footer-note {
            margin-top: 2.5rem;
            text-align: center;
            padding: 1rem 0.5rem 0.2rem;
            border-top: 2px dotted #b8dae9;
            font-size: 1rem;
            color: #1f4a5e;
            background: rgba(255, 255, 255, 0.3);
            border-radius: 60px;
            backdrop-filter: blur(2px);
            font-weight: 500;
            display: flex;
            justify-content: center;
            flex-wrap: wrap;
            gap: 0.5rem 1.2rem;
        }

        .footer-note .highlight {
            background: #f7d44a;
            padding: 0.1rem 1rem;
            border-radius: 40px;
            color: #1f3a4b;
            font-weight: 600;
        }

        .footer-note .wechat {
            background: #b1d9c5;
            padding: 0.1rem 1.2rem;
            border-radius: 40px;
            color: #0a2f2a;
            font-weight: 600;
        }

        /* 响应式微调 */
        @media (max-width: 640px) {
            body { padding: 1rem 0.8rem; }
            .container { padding: 1.2rem; }
            .header-title h1 { font-size: 1.8rem; }
            .course-grid { grid-template-columns: 1fr; }
            .card { padding: 1rem; }
        }

        /* 点缀小元素 */
        .card::after {
            content: "";
            position: absolute;
            bottom: 8px;
            right: 12px;
            font-size: 1.8rem;
            opacity: 0.08;
            pointer-events: none;
            color: #00a8cc;
        }

        /* 不同章节类别可加小图标，但保持简洁 */
        .card:nth-child(5n+1) .chapter-num { background: #f2c94c; } /* 黄 */
        .card:nth-child(5n+2) .chapter-num { background: #7ac7c4; } /* 薄荷 */
        .card:nth-child(5n+3) .chapter-num { background: #f7a58f; } /* 珊瑚 */
        .card:nth-child(5n+4) .chapter-num { background: #a3c9f0; } /* 天蓝 */
        .card:nth-child(5n+5) .chapter-num { background: #c5b4e3; } /* 淡紫 */