背景变暗，弹出提示层
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以下为页面源码:
<!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>
<title>ddd</title>
<script>
function locking(){
document.all.ly.style.display="block";
document.all.ly.style.width=document.body.clientWidth;
document.all.ly.style.height=document.body.clientHeight;
document.all.Layer2.style.display='block';
selectObjHidded();
}
function Lock_CheckForm(theForm){
if(theForm.P_USERPASS.value==''){alert("错误：请输入你的用户密码!");theForm.P_USERPASS.focus();return false;}
if(theForm.P_USERPASS.value !='123'){alert("错误：密码错误!");theForm.P_USERPASS.value='';theForm.P_USERPASS.focus();return false;}
else{document.all.ly.style.display='none';document.all.Layer2.style.display='none';}
selectObjVisible();
return false;
}
/**
* 隐藏所有的select
*/
function selectObjHidded(){
var obj;
obj=document.getElementsByTagName("SELECT");
var i;
for(i=0;i<obj.length;i++) obj[i].style.visibility="hidden";
}
/**
* 显示所有的select
*/
function selectObjVisible(){
var obj;
obj=document.getElementsByTagName("SELECT");
var i;
for(i=0;i<obj.length;i++) obj[i].style.visibility="visible";
}
</script>
<style type="text/css">
<!--
body {background-color: #00FFFF;}
-->
</style>
</head>
<body>
<p align="center">
<img src="http://gg.blueidea.com/2006/chinaok/468x60.gif">
<SELECT ID="oSelect" NAME="Cars" SIZE="3" MULTIPLE>
<OPTION VALUE="1" SELECTED>宝马
<OPTION VALUE="2">保时捷
<OPTION VALUE="3" SELECTED>奔驰
</SELECT>
</p>
<p align="center">
<INPUT TYPE="button" value="系统锁定" onclick="locking()">
</p>
<div id="ly" style="position:absolute;top:0px;FILTER: alpha(opacity=60);background-color:#777; z-index:2;left: 0px;display:none;"></div>
<!-- 浮层框架开始 -->
<div id="Layer2" align="center" style="position:absolute; z-index:3; width: 540; height:170px;left:expression((document.body.offsetWidth-540)/2); top: expression((document.body.offsetHeight-170)/2);background-color:#fff;display:none;" valign="center">
<form method="POST" action="" onsubmit="return Lock_CheckForm(this);">
<TABLE width=540 height=170 border=0 cellpadding=0 cellspacing=0 style="border:0 solid #e7e3e7;border-collapse: collapse">
<TR>
<TD style="background-color:#73A2d6;color:#fff;padding-left:4px;padding-top:2px;font-weight:bold;font-size:14px;" height=27 valign="center">[ 警 告 ]</TD>
</TR>
<TR>
<TD align="center" valign="center">请输入解除锁定密码<p><input type="text" name="P_USERPASS" size="20"></TD>
</TR>
<TR>
<TD height=30 align="center"><INPUT type="submit" value=" 确 定 "></TD>
</TR>
</TABLE>
</form>
</div>
<!-- 浮层框架结束 -->
</body>
</html>
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