在线运行代码 - 菜鸟教程

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8"> 
<title>菜鸟教程(cainiaoplay.com)</title>
<style>p:only-child
{
background:#ff0000;
}
</style>
</head>
<body>

<div><p>This is a paragraph.</p></div>

<div><span>This is a span.</span><p>This is a paragraph.</p></div>

<p><b>注意:</b> Internet Explorer 8以及更早版本的浏览器不支持 :only-child选择器.</p>

</body>
</html>

源代码

动行结果