<style>
#div1{
width:200px;
height:200px;
background-color:#F00;
}
#div2{
width:50px;
height:50px;
background:#FF0;
position:relative;
left:75%;
top:75%;
}
</style>
</head>
<body>
<div id="div1">
<div id="div2"></div>
</div>
<body>
<html>
原文：http://www.cnblogs.com/qinxuemei/p/3980238.html