css属性实例:两个div边框内外嵌套，代码如下：
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gbk" />
<title>css属性实例</title>
<style>
.main{
border:2px solid #333333;}
.include{
margin:50px;
border:2px solid #333333;
width:500px;
height:50px;
}
</style>
</head>
<body>
<div class="main"><div class="include"></div></div>
</body>
</html>