main中的righ块，增加了右浮动，margin-left就不起作用了
<!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{background:grey;height:100px;}
.main{background:red;height:400px;}
.left{ background:blue;width:200px;position:absolute;left:0;top:100px;height:400px;}
.right{background:green;float:right;margin-left:210px;height:400px;}
.foot{clear:both;background:orange;}
</style>
</head>
<body>
<div class="top">top</div>
<div class="main">
<div class="right">right</div>
<div class="left">left</div>
</div>
<div class="foot">foot</div>
</body>
</html>
谁能给我解析下为什么？
浮动不是也是成为了一个块吗？为何做外边距没有作用了？
