自适应布局(四种写法，三种方案)
1、使用position：absolute.
<!doctype html>
<html>
<head>
<style>
body{
width: 100%;
padding: 0;
margin: 0;
}
div{
height: 500px;
}
.div1{
width: 100px;
background: red;
float: left;
}
.div2{
height: 500px;
background: blue;
position: absolute;
left: 100px;
right: 100px;
}
.div3{
width: 100px;
background: green;
float: right;
}
</style>
</head>
<body>
<div class="div1">i</div>
<div class="div2">ii</div>
<div class="div3">iii</div>
</body>
</html>
优点实现简单，缺点由于使用absolute性能不好。也可以使最左和最右的div绝对定位。
<!doctype html>
<html>
<head>
<style>
body{
width: 100%;
padding: 0;
margin: 0;
}
div{
height: 500px;
}
.div1{
width: 100px;
background: red;
position: absolute;
left: 0;
top:0;
}
.div2{
margin: 0 100px;
background: blue;
}
.div3{
width: 100px;
background: green;
position: absolute;
right: 0;
top:0;
}
</style>
</head>
<body>
<div class="div1">i</div>
<div class="div2">ii</div>
<div class="div3">iii</div>
</body>
</html>
2、使用margin负值法。该方法中间元素需放在最前面，而且里面包含两层div，难以理解。
<!doctype html>
<html>
<head>
<style>
body{
width: 100%;
padding: 0;
margin: 0;
}
div{
height: 500px;
}
.div1{
width: 100px;
background: red;
float: left;
margin-left: -100%;
}
.div2{
width: 100%;
float: left;
background: blue
}
.div2 div{
margin: 0 100px;
}
.div3{
width: 100px;
background: green;
float: right;
margin-left: -100px;
}
</style>
</head>
<body>
<div class="div2"><div>ii</div></div>
<div class="div1">i</div>
<div class="div3">iii</div>
</body>
</html>
3、使用自身浮动。该方法中间的只能放在后面。
<!doctype html>
<html>
<head>
<style>
body{
width: 100%;
padding: 0;
margin: 0;
}
div{
height: 500px;
}
.div1{
width: 200px;
background: red;
float: left;
}
.div2{
margin: 0 200px;
background: blue;
}
.div3{
width: 200px;
background: green;
float: right;
}
</style>
</head>
<body>
<div class="div1">i</div>
<div class="div3">iii</div>
<div class="div2">ii</div>
</body>
</html>
原文：http://my.oschina.net/zhangstephen/blog/335950