请问为什么head和top做出来不同？
<!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>无标题文档</title>
<style type="text/css">
body{margin:0;padding:0}
.top{height:100px;background:#C00;}
.head{height:100px;width:800px;background:#600;margin:0 auto;}
.main{width:800px;height:600px;background:#C03;margin:0 auto;}
.left{width:200px;height:600px;background:#C30;float:left;}
.right{width:600px;height:600px;background:#C60;float:right;}
.sub_l{width:400px;height:600px;background:#303;float:left;}
.sub_r{width:200px;height:600px;background:#390;float:right;}
.foot{width:800px;height:100px;background:#F0F;margin:0 auto;}
</style>
</head>
<body>
<div class="top">top
<div class="head"></div>
</div>
<div class="main">
<div class="left"></div>
<div class="right">
<div class="sub_l"></div>
<div class="sub_r"></div>
</div>
</div>
<div class="foot">foot</div>
</body>
</html>
