.left{background:blue;width:200px;height:190px;position:absolute;left:0;top:0; }在left选择器中为什么用“left:0,top:0”来设置位置，而在right选择器中用“margin-left”设置？
<!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:#ccc;height:50px;}
.main{width:100%;background:red;height:190px;position:relative;}
.left{background:blue;width:200px;height:190px;position:absolute;left:0;top:0; }
.right{background:green;height:190px;margin-left:210px;}
.foot{background:orange;height:30px;}
</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>
