增加一个<div>元素，参照老师最开始讲的一个混合布局来做
<!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>混合布局编程挑战</title>
<style type="text/css">
body{ margin:0; padding:0; font-size:30px; color:#fff}
.top{background:gray;}
.main{background:red;position:relative;}
.left{ background:blue; width:200px;position:absolute;height:600px;top:0;left:0;}
.right{background:green;height:600px;margin:0 0 0 210px;}
.foot{background:orange;}
.sui{position:absolute;top:0;right:0;}
</style>
</head>
<body>
<div class="top">top</div>
<div class="main">
<div class="right">right</div>
<div class="left">left</div>
<div class="sui"></div>
</div>
<div class="foot">foot</div>
</body>
</html>
