http://jsfiddle.net/hdrenollet/dsbSt/embedded/result/
如果我理解正确,您正在寻找这样的东西:
<head>
<title></title>
<script>
</script>
<style>
#parent{
width:100%;
}
#columnleft{
position:relative;
float:left;
border: 1px solid black;
top:0px;
width:150px;
height: 400px;
}
#content{
position:relative;
width:100%;
top:0px;
padding: 20px;
margin-left:150px;
margin-right:200px;
}
#columnright{
border: 1px solid black;
float:right;
top:0px;
width:200px;
height: 400px;
}
</style>
</head>
<body>
<div id="parent">
<div id="columnleft"></div>
<div id="columnright"></div>
<div id="content">Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aenean lectus sem, lobortis fermentum eleifend non, interdum at orci. Ut nec mauris vulputate, eleifend elit vitae, suscipit felis. Etiam leo ligula, pellentesque non urna sed, sagittis hendrerit nibh. Sed pharetra pellentesque nunc vitae imperdiet. orci. Nam ac nisi sed ipsum ullamcorper aliquet eget lobortis enim. Duis consequat sed arcu vel vulputate. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Phasellus mollis porttitor sapien. Duis a sodales justo. Mauris gravida aliquet nunc in scelerisque. Lorem ipsum dolor sit amet, consectetur adipiscing elit. Sed vel nunc sagittis, dapibus quam eu, congue magna.</div>
</div>
</body>
您需要将内容容器的 margin-left 和 margin-right 设置为左右列的宽度。