/* ================= 导航栏主体 ================= */
        .header {
            position: fixed;
            top: 0; left: 0; right: 0;
            height: 70px;
            background-color: #ffffff; /* 初始白底 */
            box-shadow: 0 2px 10px rgba(0,0,0,0.05);
            z-index: 1000;
            
            /* ✨ 纯CSS实现滚动变透明 (现代浏览器原生支持) */
            animation: scroll-fade linear forwards;
            animation-timeline: scroll();
        }

        /* 滚动动画关键帧：滚动超过5%后变为透明+毛玻璃 */
        @keyframes scroll-fade {
            0% { 
                background-color: #ffffff; 
                box-shadow: 0 2px 10px rgba(0,0,0,0.05); 
                backdrop-filter: blur(0px);
            }
            5%, 100% { 
                background-color: rgba(255, 255, 255, 0.7); 
                box-shadow: none; 
                backdrop-filter: blur(12px); 
                -webkit-backdrop-filter: blur(12px);
            }
        }

        .header-inner {
            max-width: 1380px;
            margin: 0 auto;
            padding: 0 32px;
            height: 100%;
            display: flex;
            align-items: center;
            justify-content: space-between;
            position: relative;
        }

        /* 隐藏纯CSS控制开关 (核心技巧) */
        .menu-toggle-checkbox {
            display: none;
        }

        /* ================= LOGO ================= */
        .logo {
            font-size: 20px;
            font-weight: 700;
            color: #111111; 
            text-decoration: none;
            letter-spacing: -1px;
            transition: opacity 0.3s;
            z-index: 2;
        }
        .logo:hover { opacity: 0.8; }
        .logo span { color: #2563eb; }

        /* ================= 导航链接 ================= */
        .nav {
            display: flex;
            align-items: center;
            gap: 36px;
        }

        .nav-link {
            font-size: 15px;
            font-weight: 500;
            color: #333333; 
            text-decoration: none;
            position: relative;
            padding: 4px 0;
            transition: color 0.3s;
        }

        .nav-link::after {
            content: '';
            position: absolute;
            bottom: 0; left: 0;
            width: 0; height: 2px;
            background-color: #111111;
            transition: width 0.3s ease;
        }
        .nav-link:hover { color: #000000; }
        .nav-link:hover::after { width: 100%; }

        /* ================= 右侧按钮 ================= */
        .nav-btn {
            padding: 10px 26px;
            background-color: #84061e; 
            color: #ffffff !important; 
            border-radius: 8px;
            font-weight: 600;
            font-size: 14px;
            transition: all 0.3s ease;
        }
        .nav-btn::after { display: none; }
        .nav-btn:hover {
            background-color: #333333;
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(0,0,0,0.15);
        }

        /* ================= 移动端菜单按钮 ================= */
        .mobile-toggle {
            display: none;
            background: none; border: none;
            font-size: 28px; color: #111;
            cursor: pointer;
            z-index: 2;
            user-select: none;
        }
        .icon-close { display: none; } /* 默认隐藏关闭图标 */

        /* ================= 页面演示内容 ================= */
        .hero {
            height: 100vh;
            display: flex; flex-direction: column;
            align-items: center; justify-content: center;
            background: linear-gradient(180deg, #e0e7ff 0%, #f8f9fa 100%);
            text-align: center;
            padding: 0 20px;
        }
        .hero h1 { font-size: 48px; color: #111; margin-bottom: 16px; font-weight: 800; }
        .hero p { font-size: 18px; color: #555; max-width: 600px; line-height: 1.6; }
        .scroll-hint {
            margin-top: 40px; font-size: 14px; color: #888;
            animation: bounce 2s infinite;
        }
        @keyframes bounce {
            0%, 100% { transform: translateY(0); }
            50% { transform: translateY(10px); }
        }

        .section-2, .section-3 {
            height: 100vh;
            display: flex; align-items: center; justify-content: center;
            border-top: 1px solid #eee;
        }
        .section-2 { background: #ffffff; }
        .section-3 { background: #f0fdf4; }
        .section-2 h2, .section-3 h2 { font-size: 32px; color: #333; }

        /* ================= 移动端响应式 (纯CSS实现) ================= */
        @media (max-width: 768px) {
            .header {           
            height: 60px;
        }
            .mobile-toggle { 
                display: block; 
            }
            .logo {
            font-size: 14px;
        }
            .nav { 
                display: none; /* 默认隐藏菜单 */
                position: absolute; 
                top: 72px; left: 0; right: 0;
                background: #ffffff;
                flex-direction: column;
                padding: 20px 32px;
                gap: 20px;
                box-shadow: 0 10px 20px rgba(0,0,0,0.05);
            }
            
            /* ✨ 核心：通过 checkbox 选中状态控制菜单显示 (纯CSS) */
            .menu-toggle-checkbox:checked ~ .header-inner .nav {
                display: flex;
            }
            
            /* 切换图标显示状态 */
            .menu-toggle-checkbox:checked ~ .header-inner .mobile-toggle .icon-open { display: none; }
            .menu-toggle-checkbox:checked ~ .header-inner .mobile-toggle .icon-close { display: block; }
            
            .nav-btn { width: 100%; text-align: center; }
            .hero h1 { font-size: 32px; }
        }