双飞翼布局：直接上代码,不做过多解释，自己敲一遍就理解了！
<div class="wrap">
<div class="main">
<div class="mainin">main</div>
</div>
<div class="left">left</div>
<div class="right">right</div>
</div>
<style>
.main,
.left,
.right {
float: left;
height: 200px;
}
.main {
width: 100%;
background: #ace;
}
.left {
width: 20%;
background: #eee;
margin-left: -100%;
}
.right {
width: 30%;
background: #ddd;
margin-left: -30%;
}
.mainin {
margin: 0 30% 0 20%;
}
</style>
