<!DOCTYPE html>
<html>
<head>
<style>
li:first-child {
background: yellow;
}
</style>
</head>
<body>
<h1>:first-child 实例</h1>
<ul>
<li>咖啡</li>
<li>茶</li>
<li>可口可乐</li>
</ul>
<ol>
</ol>
</body>
</html>