让div 充满整个body
<head>
<title>网上在线客服系统</title>
<style type="text/css">
#mainDiv { background-color:Green; height:100% ; width:100%; position:absolute;}
body { background-color:Yellow; margin:0px; padding:0px; overflow:hidden;}
</style>
</head>
<body>
<div id="mainDiv">
</div>
</body>
</html>
