/* 全局重置 & 柔和风格 */
        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            font-family: 'Segoe UI', Roboto, system-ui, -apple-system, sans-serif;
            background: linear-gradient(145deg, #f7faff 0%, #eef3fc 100%);
            min-height: 100vh;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
            padding: 2rem 1.5rem;
        }

        /* 主卡片 – 磨砂玻璃质感 */
        .index-card {
            max-width: 1000px;
            width: 100%;
            background: rgba(255, 255, 255, 0.6);
            backdrop-filter: blur(8px);
            -webkit-backdrop-filter: blur(8px);
            border-radius: 48px;
            padding: 2.8rem 2.5rem 3.2rem;
            box-shadow: 0 30px 50px -20px rgba(0, 20, 40, 0.25),
                        0 8px 24px rgba(0, 0, 0, 0.04);
            border: 1px solid rgba(255, 255, 255, 0.5);
            transition: all 0.2s ease;
        }

        h1 {
            font-size: 2.6rem;
            font-weight: 600;
            letter-spacing: -0.02em;
            color: #0b2b4a;
            display: flex;
            align-items: center;
            gap: 0.5rem;
            margin-bottom: 0.4rem;
        }

        h1 small {
            font-size: 1rem;
            font-weight: 400;
            color: #2c5778;
            background: rgba(60, 110, 160, 0.10);
            padding: 0.2rem 1rem;
            border-radius: 40px;
            letter-spacing: 0.3px;
            margin-left: 0.75rem;
        }

        .subhead {
            font-size: 1.1rem;
            color: #2f5577;
            border-left: 4px solid #4c8bcb;
            padding-left: 1.2rem;
            margin-bottom: 2.8rem;
            font-weight: 350;
            opacity: 0.9;
        }

        /* 链接卡片网格 — 响应式 */
        .link-grid {
            display: grid;
            grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
            gap: 1.8rem;
            margin: 1.2rem 0 1.8rem;
        }

        /* 每一个链接都是块级卡片 */
        .link-item {
            display: block;
            background: rgba(255, 255, 255, 0.5);
            backdrop-filter: blur(4px);
            -webkit-backdrop-filter: blur(4px);
            border-radius: 32px;
            padding: 1.8rem 1rem 1.6rem;
            text-decoration: none;
            color: #0e2c44;
            border: 1px solid rgba(255, 255, 255, 0.8);
            box-shadow: 0 6px 14px rgba(0, 20, 30, 0.04);
            transition: all 0.2s cubic-bezier(0.2, 0.9, 0.4, 1);
            text-align: center;
            font-weight: 500;
            font-size: 1.2rem;
            letter-spacing: 0.3px;
            position: relative;
            min-height: 100px;
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
        }

        /* 每个卡片的小图标/装饰 */
        .link-item::before {
            content: "⚡";
            font-size: 2rem;
            display: block;
            margin-bottom: 0.4rem;
            filter: drop-shadow(0 2px 4px rgba(0,0,0,0.02));
        }

        /* 不同实验单独微调图标 (保留趣味性) */
        .link-item[data-lab="newton"]::before { content: "🍎"; }
        .link-item[data-lab="optics"]::before { content: "🔦"; }
        .link-item[data-lab="thermo"]::before { content: "🌡️"; }
        .link-item[data-lab="wave"]::before { content: "〰️"; }
        .link-item[data-lab="electro"]::before { content: "⚡"; }
        .link-item[data-lab="quantum"]::before { content: "🌀"; }

        /* 悬停 & 焦点效果 */
        .link-item:hover,
        .link-item:focus-visible {
            transform: translateY(-6px) scale(1.01);
            background: rgba(255, 255, 255, 0.8);
            backdrop-filter: blur(8px);
            border-color: #b6d4f0;
            box-shadow: 0 20px 32px -12px rgba(24, 80, 140, 0.25);
            color: #00315e;
        }

        .link-item:active {
            transform: scale(0.97) translateY(-2px);
            transition-duration: 0.04s;
        }

        /* 特殊标记 – 牛顿第二定律 (突出) */
        .link-item.highlight {
            background: rgba(220, 240, 255, 0.7);
            border-left: 4px solid #1f7fcf;
            border-right: 4px solid #1f7fcf;
            box-shadow: 0 8px 18px rgba(31, 127, 207, 0.12);
        }

        .link-item.highlight:hover {
            background: rgba(200, 230, 255, 0.8);
            border-color: #1f7fcf;
            box-shadow: 0 16px 32px -8px rgba(31, 127, 207, 0.25);
        }

        .link-item .badge {
            font-size: 0.7rem;
            background: #1f7fcf;
            color: white;
            padding: 0.15rem 0.8rem;
            border-radius: 40px;
            letter-spacing: 0.4px;
            margin-top: 0.5rem;
            opacity: 0.7;
            font-weight: 400;
        }

        /* 页脚辅助信息 */
        .footer-note {
            margin-top: 2.5rem;
            font-size: 0.95rem;
            color: #3e6080;
            border-top: 1px solid rgba(60, 100, 150, 0.12);
            padding-top: 1.8rem;
            display: flex;
            flex-wrap: wrap;
            justify-content: space-between;
            align-items: center;
        }

        .footer-note span {
            background: rgba(60, 110, 170, 0.04);
            padding: 0.2rem 1rem;
            border-radius: 40px;
        }

        .footer-note code {
            background: #eaf0f8;
            padding: 0.2rem 0.8rem;
            border-radius: 24px;
            font-size: 0.85rem;
            color: #17426b;
        }

        /* 响应式微调 */
        @media (max-width: 600px) {
            .index-card {
                padding: 1.8rem 1.2rem;
                border-radius: 32px;
            }
            h1 {
                font-size: 2rem;
                flex-wrap: wrap;
            }
            h1 small {
                margin-left: 0;
                font-size: 0.85rem;
            }
            .subhead {
                font-size: 1rem;
                padding-left: 0.8rem;
            }
            .link-grid {
                gap: 1.2rem;
                grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
            }
            .link-item {
                padding: 1.4rem 0.8rem;
                font-size: 1rem;
                min-height: 80px;
            }
            .link-item::before {
                font-size: 1.8rem;
            }
        }

        @media (max-width: 420px) {
            .link-grid {
                grid-template-columns: 1fr 1fr;
                gap: 0.8rem;
            }
            .link-item {
                min-height: 70px;
                padding: 1rem 0.4rem;
                font-size: 0.95rem;
                border-radius: 24px;
            }
        }

        /* 简单的进入动画 */
        .index-card {
            animation: fadeUp 0.6s ease-out forwards;
        }

        @keyframes fadeUp {
            0% { opacity: 0; transform: translateY(20px); }
            100% { opacity: 1; transform: translateY(0); }
        }

        /* 链接里的小字 */
        .link-item .sub {
            font-size: 0.7rem;
            font-weight: 300;
            color: #3a6383;
            margin-top: 0.2rem;
            opacity: 0.7;
        }