以下代码复制粘贴即可使用：
示例一： <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta charset="gb2312" />
<style type="text/css">
.page_center {
width:100%;
}
#nav {
background-color:red;
height:20px;
}
#left {
width:120px;
background-color:green;
position:absolute;
}
#middle {
background-color:yellow;
}
#right {
width:120px;
background-color:green;
position:absolute;
top:0;
right:0;
}
#foot {
background-color:pink;
}
#main {
position:relative;
}
</style>
</head>
<body>
<div id="nav" class="page_center">上边</div>
<div id="main" class="page_center">
<div id="left">左边</div>
<div id="middle"> 中间部分</div>
<div id="right">右边</div>
</div>
<div id="foot" class="page_center">底边</div>
</body>
</html>
示例2： <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Untitled Document</title>
</head>
<style type="text/css">
#left{
float:left; width:240px; height:500px; background:#0C9;
}
#right{
float:right;width:240px;height:500px; background:#933;
}
#center{
height:500px;background:#06C;
}
</style>
<body>
<div id="left" >左边</div>
<div id="right" >右边</div>
<div id="center" style="">中间</div>
</body>
</html>
<span style="font-size: 14px; font-family: Arial, Helvetica, sans-serif;"><strong></strong></span>
