<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<style type="text/css">
#a1
{
width: 100px;
height: 100px;
float: left;
background-color: Yellow;
}
#a3
{
width: 100px;
height: 100px;
float: right;
background-color: Blue;
}
#a2
{
width: auto;
margin:0 100px;
height: 100px;
background-color: Green;
}
#all
{
min-width:370px;
}
</style>
</head>
<body>
<form id="form1" runat="server">
<div id="all" style="width: 100%">
<div id="a3">
a3
</div>
<div id="a1">
a1
</div>
<div id="a2">
a2546464564646465ty
</div>
</div>
</form>
</body>
</html>
原文：http://www.cnblogs.com/zhwl/p/4334219.html