为什么三列布局，不用两个左浮动，一个右浮动？
<!doctype html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>三列布局</title>
<style>
body{ margin:0; padding:0; font-size:30px; font-weight:bold}
div{ text-align:center; line-height:50px}
.left{ width:20%; height:600px; background:#ccc;float:left;}
.main{ height:600px;width:60%; background:#9CF;float:left;}
.right{ height:600px; width:20%;background:#FCC;float:right;}
</style>
</head>
<body>
<div>left</div>
<div>main</div>
<div>right</div>
</body>
</html>
