<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<style>
#div1 .text{
color: red;
}
#div2 .text{
color: yellow;
}
</style>
<title>类选择器</title>
</head>
<body>
<div id="div1">
<p class="text">这是黄色</p>
</div>
<p class="q"></p>
<p class="w"></p>
<p class="e"></p>
<p class="r"></p>
<div id="div2">
<p class="text">这是红色</p>
</div>
</body>
</html>
原文：http://www.cnblogs.com/ronghtp/p/7647318.html