div+css遮罩事例
<!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=gb2312" />  
<title>弹出提示</title>  
<style>  
* {margin:0;padding:0;font-size:12px;}  
html,body {height:100%;width:100%;}  
#content {background:#f8f8f8;padding:30px;height:100%;}  
#content a {font-size:30px;color:#369;font-weight:700;}  
#alert {border:1px solid #369;width:300px;height:150px;background:#e2ecf5;z-index:1000;position:absolute;display:none;}  
#alert h4 {height:20px;background:#369;color:#fff;padding:5px 0 0 5px;}  
#alert h4 span {float:left;}  
#alert h4 span#close {margin-left:210px;font-weight:500;cursor:pointer;}  
#alert p {padding:12px 0 0 30px;}  
#alert p input {width:120px;margin-left:20px;}  
#alert p input.myinp {border:1px solid #ccc;height:16px;}  
#alert p input.sub {width:60px;margin-left:30px;}  
</style>
</head>
<body>  
<div id="content">  
<a href="#">注册</a>  
</div>  
<div id="alert">  
<h4><span>现在注册</span><span id="close">关闭</span></h4>  
<p><label>用户名</label><input type="text" class="myinp" onmouseover="this.style.border='1px solid #f60'" onfoucs="this.style.border='1px solid #f60'" onblur="this.style.border='1px solid #ccc'" /></p>  
<p><label>密 码</label><input type="password" class="myinp" onmouseover="this.style.border='1px solid #f60'" onfoucs="this.style.border='1px solid #f60'" onblur="this.style.border='1px solid #ccc'" /></p>  
<p><input type="submit" value="注册" class="sub" /><input type="reset" value="重置" class="sub" /></p>  
</div>  
<script type="text/javascript">  
var myAlert = document.getElementById("alert");  
var reg = document.getElementById("content").getElementsByTagName("a")[0];  
var mClose = document.getElementById("close");  
reg.onclick = function()  
{  
myAlert.style.display = "block";  
myAlert.style.position = "absolute";  
myAlert.style.top = "50%";  
myAlert.style.left = "50%";  
myAlert.style.marginTop = "-75px";  
myAlert.style.marginLeft = "-150px";
mybg = document.createElement("div");  
mybg.setAttribute("id","mybg");  
mybg.style.background = "#000";  
mybg.style.width = "100%";  
mybg.style.height = "100%";  
mybg.style.position = "absolute";  
mybg.style.top = "0";  
mybg.style.left = "0";  
mybg.style.zIndex = "500";  
mybg.style.opacity = "0.3";  
mybg.style.filter = "Alpha(opacity=30)";  
document.body.appendChild(mybg);
document.body.style.overflow = "hidden";  
}
mClose.onclick = function()  
{  
myAlert.style.display = "none";  
mybg.style.display = "none";  
}  
</script>  
</body&g