javascript 难题 div嵌套的点击事件

一定要嵌套吗？外内，只要设置大小和位置就行了
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312">
<meta name="Keywords" content="51windows.Net">
<META NAME="Author" CONTENT="haiwa">
<title>New Document -51windows.Net</title>
<style>
<!--
*         {font:menu}
-->
</style>
</head><body>
<SCRIPT LANGUAGE="JavaScript">
<!--
function hide_show(obj)
{
if (obj.style.display=="none")
{
obj.style.display=""
}
else
{
obj.style.display="none"
}
}
//-->
</SCRIPT>
<div id=test1 style="position: absolute; top: 0; left: 0; width: 200; height: 200;background:blue;display:none">
</div>
<div style="position: absolute; top: 50; left: 50; width: 100; height: 100;background:green;" onmouseover=this.style.background="yellow"  onmouseout=this.style.background="green" onclick=hide_show(test1)>
  www
</div>
</body></html>