当鼠标移出灰色区域时候,菜单项怎么隐藏起来

<!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=utf-8" /> <title>无标题文档</title> <script language="javascript"> var $=function(id){ return document.getElementById(id); } function hover(){ if($('hover').style.display == 'none'){ $('hover').style.display = ''; }else{ $('hover').style.display = 'none'; } } </script> <style> *{margin:10px; padding:0} #nav{border:#ccc 1px solid; height:25px; width:198px; text-align:center; line-height:25px; margin-bottom:0} #hover{ position:absolute; height:100px; width:200px; margin-top:-2px; text-align:center; background-color:#ccc; } </style> </head> <body> 鼠标移上来 <ul> <li>菜单一</li> <li> 菜单二</li> </ul> </body> </html>
[Ctrl+A 全选 注:如需引入外部Js需刷新才能执行]