CSS 3层嵌套居中布局
<html>
<head>
<style type="text/css">
.root{
background-color: red;
width: 80%;
top: 20px;
position: fixed;
bottom: 20px;
margin-left: 10%;
}
.parent{
background-color: green;
position: absolute;
left: 20px;
right: 20px;
top: 30px;
bottom: 20px;
}
.child{
background-color: blue;
position: absolute;
left: 10px;
right: 10px;
top: 20px;
height:100px;
margin-top: -65px;
}
</style>
</head>
<body>
<div class="root">
<div class="parent">
<div class="child">
</div>
</div>
</div>
</body>
</html>
