这个div的标题一定要写么？为什么我没写会没有反应。显示不出结果
<!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>一列布局</title>
<style type="text/css">
body{margin:0;padding:0}
.top{width:500px;weight:300px;background:blue;margin:0 auto}
.middle{width:600px;weight:400px;background:red;margin:0 auto}
.left{width:200px;weight:800px;background:green;float:left}
.right{width:400px;weight:800px;background:black;float:right}
.down{width:600px;weight:300px;background:yellow;margin:0 auto}
</style>
</head>
<body>
<div class="top"></div>
<div class="middle">
<div class="left"></div>
<div clasee="right"></div>
</div>
<div class="down"></div>
</body>
</html>
