<style type="text/css">
		body{
			margin:10px;
			font-family: Arial;
			font-size:13px;
		}
		#father{
			background-color:#a0c8ff;
			border:1px dashed #000000;
			width:100%;
			height:100%;
		}
		#block{
			background-color: #fff0ac;
			border:1p dashed #000000;
			padding:10px;
			position:absolute;
			left:20px;
			top:40px;
		}
	</style>
<div id="father"> <div id="block">absolute</div>

height:100%没有将容器撑开。
解决办法:
html,body{/*必须要html和body同时设置height:100%*/
  margin:10px;
  font-family: Arial;
  font-size:13px;
  height:100%;
		}

原文:http://www.cnblogs.com/yee0403/p/5095228.html