/* 头部和导航 */
        header {
            background-color: #fff;
            box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
            position: sticky;
            top: 0;
            z-index: 1000;
        }
        
        .header-container {
            display: flex;
            justify-content: space-between;
            align-items: center;
            padding: 15px 0;
        }
        
        .logo {
            display: flex;
            align-items: center;
        }
        
        .logo h1 {
            font-size: 24px;
            color: #1a5276;
            margin-left: 10px;
        }
        
        .logo-img {
            height: 50px;
        }
        
        nav ul {
            display: flex;
            list-style: none;
            position: relative;
        }
        
        nav li {
            margin-left: 30px;
            position: relative;
        }
        
        nav a {
             text-decoration: none;
            color: #2c3e50;
            font-weight: 500;
            font-size: 16px;
            transition: color 0.3s;
            padding: 8px 0;
            display: block;
        }
        
        nav a:hover {
            color: #3498db;
        }
        /* 下拉菜单样式 - 修改为垂直排列四行 */
        .dropdown-menu {
            position: absolute;
            top: 100%;
            left: 0;
            background: white;
            min-width: 200px;
            box-shadow: 0 5px 15px rgba(0, 0, 0, 0.1);
            border-radius: 4px;
            opacity: 0;
            visibility: hidden;
            transform: translateY(10px);
            transition: all 0.3s ease;
            z-index: 1000;
            display: flex;
            flex-direction: column;
        }
        
        .dropdown-menu li {
            margin: 0;
            border-bottom: 1px solid #f0f0f0;
            flex: none;
        }
        
        .dropdown-menu li:last-child {
            border-bottom: none;
        }
        
        .dropdown-menu a {
            padding: 12px 15px;
            color: #555;
            display: block;
            transition: all 0.2s;
            text-align: left;
            white-space: nowrap;
        }
        
        .dropdown-menu a:hover {
            background: #f8f9fa;
            color: #3498db;
            padding-left: 20px;
        }
        
        .has-dropdown:hover .dropdown-menu {
            opacity: 1;
            visibility: visible;
            transform: translateY(0);
        }
        
        .dropdown-toggle::after {
            content: "▼";
            font-size: 10px;
            margin-left: 5px;
            transition: transform 0.3s;
        }
        
        .has-dropdown:hover .dropdown-toggle::after {
            transform: rotate(180deg);
        }
        
        
        .mobile-menu {
            display: none;
            font-size: 24px;
            cursor: pointer;
        }