这里要实现得是，两边固定不变，变化中间的效果
实现代码如下：
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style type="text/css">
#header,#content,#footer{
background-color:#ccc;
border:1px solid #00C;
height:50px;
80%;
margin:10px auto;
}
#content{
height:500px;
}
#left{
height:500px;
100px;
float:left;
border:solid 1px #FF0;
background-color:#0C3;
}
#right{
height:500px;
100px;
float:right;
border:solid 1px #060;
background-color:#c96;
}
#cont{
height:500px;
100%;
float:left;
margin-left:-208px;
overflow:hidden;
}
#varcont{
height:500px;
border:1px solid #000;
margin-left:208px;
background-color:#CC3;
}
</style>
</head>
<body>
<div id="header"><h3>1-3-1(2)</h3></div>
<div id="content">
<div id="left"> </div>
<div id="cont"><div id="varcont"></div></div>
<div id="right">
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</div>
</div>
<div id="footer"></div>
</body>
</html>
其实实现这一效果主要是利用调整 margin的变化，来实现得。