CSS实例教程：三列自由式布局 770-1024自适应宽度
这个例子是最典型实用的上中下，并且中间分三列的css布局，有以下2个特点：
1. 中间三列效果，可以任意实现单列背景色。
2. 整体最窄770px，最宽1024px，也就是说窗口小于770xp就出底部滚动条，如果大于1024px自动屏幕居中。
最外层的wrapper把所有内容都嵌套在里边，整体相对定位。max min已经很好的控制了最窄最宽值，但对IE没有作用。如果没有其他布局的穿插，这一层其实写在body内就可以，少一层嵌套。
#wrapper{ width:auto; border:1px solid #000; min-width:770px; max-width:1024px; text-align:left; margin-left:auto; margin-right:auto; position:relative;}
wrapper 下级的 outer header footer
其中header绝对定位，footer 相对定位；outer分别对左右有130px的外边距，这是兼容非IE的关键。
#outer{ margin-left:130px; margin-right:130px; background:silver; border-left:1px solid #000; border-right:1px solid #000; color: #000;}
#header{ position:absolute; top:0; left:0; width:100%; height:70px; line-height:70px; border-bottom:1px solid #000; overflow:hidden; background:#0ff; text-align:center; font-size:xx-large}
#footer { width:100%; clear:both; line-height:50px; border-top:1px solid #000; background:#ffc; color:#000; text-align:center; position:relative;}
outer 下级的 clearheader outerwrap right clearer
clearheader 用做填补header的空白，clearer 是一个常用的填充hack用法。
outerwrap 宽为什么是99%，而不是100%？因为他的上层outer有边框，100%宽再加2个边框象素就会撑大，FF有明显效果。
right 的处理很经典，IE下解析为定位，FF下则为浮动。负边距的处理也刚好使用上outer留出的空白。
#clearheader{ height:72px;}
.outerwrap { float:left; width:99%;}
#right {
position:relative;
width:130px; float:right; left:1px;
margin-right:-129px;
}
* html #right { margin-right:-130px; margin-left:-3px}
.clearer{ height:1px; overflow:hidden; margin-top:-1px; clear:both;}
outerwrap 内的 centrecontent left clearer 就很简单了，思路类似上边说明。
<!--[if gte IE 5]> 指定IE5.0及版本以上浏览器有效
使用expression方法实现对IE5.0及以上版本的宽度条件控制。
body {width:expression( documentElement.clientWidth < 770 ? (documentElement.clientWidth == 0 ? (body.clientWidth < 770 ? "770" : "auto") : "770px") : "auto" );}
#wrapper {width:expression( documentElement.clientWidth > 1024 ? (documentElement.clientWidth == 0 ? (body.clientWidth >1024 ? "1024" : "auto") : "1024px") : "auto" );}
IE6.0和FF1.5测试通过，查看运行效果：
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "//www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="//www.w3.org/1999/xhtml">
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style type="text/css">
* { margin:0; padding:0;}
body { padding:10px 0 0 0; color:#000; background:#fff; text-align:center;}
#wrapper{ width:auto; border:1px solid #000; min-width:770px; max-width:1024px; text-align:left; margin-left:auto; margin-right:auto; position:relative;}
#outer{ margin-left:130px; margin-right:130px; background:silver; border-left:1px solid #000; border-right:1px solid #000; color: #000;}
#header{ position:absolute; top:0; left:0; width:100%; height:70px; line-height:70px; border-bottom:1px solid #000; overflow:hidden; background:#0ff; text-align:center; font-size:xx-large}
#left {
position:relative;/*ie needs this to show float */
width:130px;float:left;left:-1px;
margin-left:-129px;/*must be 1px less than width otherwise won't push footer down */
}
* html #left { margin-right:-3px;}/* 3px jog*/
* html #outer{/* 3px jog*/
margin-left:127px; margin-right:127px;}
p { margin-bottom:1em; padding:0 5px}
#right {
position:relative;/*ie needs this to show float */
width:130px; float:right; left:1px;
margin-right:-129px;/*must be 1px less than width otherwise won't push footer down */
}
* html #right { margin-right:-130px; margin-left:-3px}/* stop float drop in ie + 3px jog */
#footer { width:100%; clear:both; line-height:50px; border-top:1px solid #000; background:#ffc; color:#000; text-align:center; position:relative;}
#clearheader{ height:72px;}/*needed to make room for header*/
#centrecontent { float:right; width:100%; position:relative;}
html>body #centrecontent { margin:0 -0.5%}/*moz needs this*/
.outerwrap { float:left; width:99%;}
.clearer{ height:1px; overflow:hidden; margin-top:-1px; clear:both;}
/* mac hide\*/
* html #outer, * html #wrapper,* html #centrecontent { height:1%}
/* end hide */
</style>
<!--[if gte IE 5]>
<style type="text/css">
body {width:expression( documentElement.clientWidth < 770 ? (documentElement.clientWidth == 0 ? (body.clientWidth < 770 ? "770" : "auto") : "770px") : "auto" );}
#wrapper {width:expression( documentElement.clientWidth > 1024 ? (documentElement.clientWidth == 0 ? (body.clientWidth >1024 ? "1024" : "auto") : "1024px") : "auto" );}
</style>
<![endif]-->
</head>
<body>
<div id="wrapper">
<div id="outer">
<div id="clearheader"></div>
<div class="outerwrap">
<div id="centrecontent">
<h1>Min width of 770px and max width of 1024px</h1>
<p>centre content goes here centre content goes here : centre content
goes here centre content goes here : centre content goes here centre
content goes here : centre content goes here centre content goes here
: centre content goes here centre content goes here : centre content
goes here centre content goes here : centre content goes here centre
content goes here : centre content goes here centre content goes here
: centre content goes here centre content goes here : centre content
goes here centre content goes here : centre content goes here centre
content goes here : centre content goes here centre content goes here
: centre content goes here centre content goes here : centre content
goes here centre content goes here : centre content goes here centre
content goes here : centre content goes here centre content goes here
: centre content goes here centre content goes here : centre content
goes here centre content goes here : centre content goes here centre
content goes here : centre content goes here content goes here : </p>
</div>
<div id="left">
<p>Left content goes here : Left content goes here : Left content goes
here : Left content goes here : Left content goes here : Left content
goes goes here : Left content goes here : </p>
</div>
<div class="clearer"></div>
</div>
<!--end outer wrap -->
<div id="right">
<p>Start Right content goes here : Right content goes here : Right content
goes here : Right content goes here : Right content goes here : Right
content goes here : Right content goes here : Right content goes here
: Right content goes here : </p>
</div>
<div class="clearer"></div>
</div>
<div id="footer">Footer - | - Footer </div>
<div id="header">Header </div>
</div>
</body>
</html>