CSS关于浮动问题
<!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;margin:0 auto;background:#ccc;}
.main{height:600px;background:red;}
.left{ height:600px;width:40%;background:blue;float:left;}
.right{ height:600px;width:55%;background:green;float:right}
.foot{height:50px;background:#F90;}
</style>
</head>
<body>
<div class="top">top</div>
<div class="main">
<div class="left">left</div>
<div class="right">right</div>
</div>
<div class="foot">foot</div>
</body>
</html>
为什么我写的这个代码foot不用清除浮动，有的人却要清除foot的浮动
