为什么让left浮动起来，会发现left跑到下面了
<!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{height:100px; background-color: #FC0;}
.main{height:500px; background-color: #f00;}
.left{height:500px; width: 200px; background-color: blue;float: left;}
.right{height: 500px; margin-left: 210px;background-color: #9C9; }
.foot{height: 60px;background-color: #FF5;}
</style>
</head>
<body>
<div class="top">top</div>
<div class="main">
<div class="right">right是淡定可能差点就哈斯卡电脑；；德川家康会尽快到数据库进行销售了农村 你看了看书谁看见了圣诞sadjcklsd</div>
<div class="left">left</div>
</div>
<div class="foot">foot</div>
</body>
<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{height:100px; background-color: #FC0;}
.main{height:500px; background-color: #f00;}
.left{height:500px; width: 200px; background-color: blue;float: left;}
.right{height: 500px; margin-left: 210px;background-color: #9C9; }
.foot{height: 60px;background-color: #FF5;}
</style>
</head>
<body>
<div class="top">top</div>
<div class="main">
<div class="right">right是淡定可能差点就哈斯卡电脑；；德川家康会尽快到数据库进行销售了农村 你看了看书谁看见了圣诞sadjcklsd</div>
<div class="left">left</div>
</div>
<div class="foot">foot</div>
</body>
</html>
