三栏宽度自适应布局
1 绝对定位实现
<style type="text/css">
html,body{margin:0; height:100%;}
#left,#right{position:absolute; top:0; width:200px; height:100%;}
#left{left:0; background:#a0b3d6;}
#right{right:0; background:#a0b3d6;}
#main{margin:0 210px; background:#ffe6b8; height:100%;} 需要知道左右的宽度
</style>
<body>
<div id="left"></div>
<div id="main"></div>
<div id="right"></div>
</body>
2 margin负值实现
<style type="text/css">
html,body{margin:0; height:100%;}
#main{width:100%; height:100%; float:left;}
#main #body{margin:0 210px; background:#ffe6b8; height:100%;}
#left,#right{width:200px; height:100%; float:left; background:#a0b3d6;}
#left{margin-left:-100%;}
#right{margin-left:-200px;}
</style>
<body>
<div id="main">
<div id="body"></div>
</div>
<div id="left"></div>
<div id="right"></div>
</body>
3 浮动法
<style type="text/css">
html,body{margin:0; height:100%;}
#main{height:100%; margin:0 210px; background:#ffe6b8;}
#left,#right{width:200px; height:100%; background:#a0b3d6;}
#left{float:left;} 左边左浮动，右边右浮动，不浮动的放中间
#right{float:right;}
</style>
<body>
<div id="left"></div>
<div id="right"></div>
<div id="main"></div>
</body>
