混合布局，为什么foot板块不显示颜色？？
<!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>三列布局</title>
<style type="text/css">
body{ margin:0; padding:0; font-size:30px; font-weight:bold}
div{ line-height:50px}
.top{height:80px;background:yellow;text-align:center;}
.body{width:800px;height:500px;background:#ccc;margin:0 auto;}
.left{ height:500px; width:400px;background:#ccc;float:left; margin:0; left:80px;text-align:center;}
.right{ height:500px; width:400px;background:#FCC;float:right;text-align:center;}
.foot{width:800px; height:100px; background:blue; margin:0 auto;text-align:center;}
</style>
</head>
<body>
<div class="top">top</div>
<div class="body">
<div class="left">left</div>
<div class="right">right</div>
<div>
<div class="foot">foot</div>
</body>
</html>
