这都是问题,但这是一个简单的例子
<!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" xml:lang="en" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html;charset=iso-8859-1" />
<title>TEST</title>
</head>
<body style="margin:0;padding:0">
<div style="background-color:#eeeeee;margin:auto;height:500px;width:500px">
<div style="position:relative">
<span style="position:absolute;display:block;height:250px;width:250px;background:green;z-layer:2"><br /><br />Should be on top</span>
</div>
<span style="position:relative;display:block;width:500px;background:blue;z-layer:1">Actually on top</span>
</div>
</body>
</html>