middle的设置不是自适应居中，只是文本，为什么
<title>三列布局</title>
<style typs="text/css">
body{margin:0;padding:0;font-size:30px;font-weight:blod}
.left{weight:200px;height:500px;background:#ccc;position:absolute;top:0;left:0}
.middle{height::500px;background:#3F9;margin:0px 310px 0px 210px;}
.right{weight:300px;height:500px;background:#CF0;position:absolute;right:0;top:0;}
</style>
</head>
<body>
<div class="left">200px</div>
<div class="middle">好多内容要居中</div>
<div class="right">300px</div>
</body>
</html>
