这里主要用到的是position:absolute;及margin属性;代码很简单，一看就明白。
<!DOCTYPE html>
<html lang="zh_CN">
<head>
<meta charset="UTF-8">
<title>三列布局,左右固定值,中间自适应</title>
<style type="text/css">
.container{position: relative;}
.left{position:absolute;left:0;top:0;width: 200px;height:500px;background-color: #f34;}
.right{position: absolute;right: 0;top:0;width: 300px;height:500px;background-color: #fcc;}
.middle{margin:0 300px 0 200px;height:500px;background-color: #ccc;}
</style>
</head>
<body>
<div class="container">
<div class="left"></div>
<div class="middle">
Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod
tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam,
quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo
consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse
cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non
proident, sunt in culpa qui officia deserunt mollit anim id est laborum.
</div>
<div class="right"></div>
</div>
</body>
</html>
那么它呈现在页面上的样子则是这样的