/* 未格式化的 CSS 示例 */ .header{background:#2c3e50;color:white;padding:20px 0;text-align:center}.nav{display:flex;justify-content:center;list-style:none}.nav li{margin:0 15px}.nav a{color:#ecf0f1;text-decoration:none;font-weight:bold}.nav a:hover{color:#3498db}@media (max-width:600px){.nav{flex-direction:column}}