盒子尺寸父子传递及嵌套Demo

 <!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>
 <meta http-equiv="Content-Type" content="text/html; charset=gb2312" />
 <title>无标题文档</title>
 <style type="text/css">
 <!--
 html,body{
 height:100%;
 }
 .box1 {
     background-color: #0000FF;
     height:100%;
     position:relative;
 }
 .box2 {
     background-color: #00FFFF;
     height:90%;
     width:90%;
     left:5%;
     top:5%;
     position:absolute;
 }
 .box3 {
     background-color: #FFFF00;
     height:20%;
     width:20%;
     right:5%;
     bottom:5%;
     position:absolute;
 }
 -->
 </style>
 </head>
 <body>
 <div class="box1">
   <div class="box2">
     <div class="box3"></div>
   </div>
 </div>
 </body>
 </html>