​x
 
<!DOCTYPE html>
<html>
<head>
<style>
p:first-child i
{
background:yellow;
}
</style>
</head>
​
<body>
​
<p>I am a <i>strong</i> man. I am a <i>strong</i> man.</p>
<p>I am a <i>strong</i> man. I am a <i>strong</i> man.</p>
​
<p><b>注释：</b>对于 IE8 及更早版本的浏览器中的 :first-child，必须声明 &lt;!DOCTYPE&gt;。</p>
​
</body>
</html>
​