<body>
<div id="main">
<div id="mainContainer">mainContainer</div>
</div>
<div id="left">
<div id="leftContainer">leftContainer</div>
</div>
<div id="right">
<div id="rightContainer">rightContainer</div>
</div>
</body>
#main{width: 100%;float: left;background-color: purple;color: #ffffff;}
#mainContainer{height: 200px;margin:0 230px;}
#left{width: 230px;height: 200px;margin-left:-100%;float: left;background-color: orange;}
#right{width: 230px;height: 200px;margin-left: -230px;float: left;background-color: pink;}
原文：http://www.cnblogs.com/applejp/p/4180726.html