<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>demo</title>
<style type="text/css">
.sub{
float: left;
width: 190px;
margin-left: -100%;
}
.main{
float:left;
width:100%;
}
.extra{
float:left;
width:230px;
margin-left: -230px;
}
.main-wrap{
margin:0 230px 0 190px;
}
</style>
</head>
<body>
<div id="page">
<div id="hd">Header</div>
<div id="bd">
<div class="main">
<div class="main-wrap">
<p>Main</p>
</div>
</div>
<div class="sub">
<p>Sub</p>
</div>
<div class="extra">
<p>Extra</p>
</div>
</div>
<div id="fd">
<p>footer</p>
</div>
</div>
</body>
</html>
优点，优先加载mian区域的内容，中间区域可根据屏幕尺寸变化自动伸缩，左右两栏则固定布局。
原文：http://www.cnblogs.com/YutaoZhou/p/6675287.html