js css 实现遮罩层覆盖其他页面元素附图

<div style=" position: fixed; width: 100%; height: 100%; 
left: 0px; top: 0px; background-color: Black; z-index: 9999; filter: alpha(opacity=70); Opacity:0.7;"></div>

z-index 必须大于遮罩元素

demo

<!doctype html> 
<html> 
<head> 
<meta charset="utf-8"> 
<title>无标题文档</title> 

<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1" /> 
<meta name="apple-mobile-web-app-capable" content="yes" /> 
<script type="text/javascript" src="jquery-1.7.2.min.js"></script> 
<style type="text/css"> 
ul, ul ul { 
list-style-type:none; 
margin: 0; 
padding: 0; 
width: 15em; 
} 

ul a { 
display: block; 
text-decoration: none; 
} 

ul li { 
margin-top: 1px; 
} 

ul li a { 
background: #333; 
color: #fff; 
padding: 0.5em; 
} 

ul li a:hover { 
background: #000; 
} 

ul li ul li a { 
background: #ccc; 
color: #000; 
padding-left: 20px; 
} 

ul li ul li a:hover,ul li ul .current a { 
background: #aaa; 
border-left: 5px #000 solid; 
padding-left: 15px; 
} 

</style> 
</head> 

<body> 
<div id="bb" style="background-color: red;display:none;z-index: 99999; max-height:79.3%; position: fixed; filter: alpha(opacity=70); Opacity:0.7; top: 10px; left:5px;"> 
<ul> 
<li> 
<a href="">老大</a> 
<ul> 
<li> 
<a href="javascript:alert('you can do you want');">老大大</a> 
<li> 
<li> 
<a href="javascript:alert('you can do you want');">老大二</a> 
<li> 
<li> 
<a href="javascript:alert('you can do you want');">老大三</a> 
<li> 
<li> 
<a href="javascript:alert('you can do you want');">老大四</a> 
<li> 
</ul> 
<li> 
<li> 
<a href="javascript:alert('you can do you want');">老二</a> 
<li> 
<li> 
<a href="javascript:alert('you can do you want');">老三</a> 
<li> 
<li> 
<a href="">老四</a> 
<ul > 
<li><a href="javascript:alert('you can do you want');">老一</a><li> 
</ul> 
<li> 
</ul> 
</div> 
<br> 
<br> 
<br> 
<br> 
<br> 
<br> 

<br> 
<br><br><br> 
<br> 
<br> 
<button id="aa">哈哈</button> 
<div id="zz" style="display:none;position: fixed; width: 100%; height: 100%; 
left: 0px; top: 0px; background-color: Black; z-index: 1999; filter: alpha(opacity=70); Opacity:0.7;"></div> 
</body> 
<script type="text/javascript"> 
$(function(){ 
$("#aa").click(function(){ 
$("#zz").show(); 
$("#bb").show(); 
$("#bb").animate({left:'100px'}); 
$("#bb").animate({left:'0px'}); 
}); 
$("#zz").click(function(){ 
$("#bb").animate({left:'-240px'}); 
$("#zz").hide(); 
}); 
$('#bb ul li ul').hide(); 
$("#bb ul li a").click(function(){ 
var a= $(this); 
var nextobj=a.next(); 
if(nextobj.is("ul")){ 
$('#bb ul li ul:visible').slideUp('normal'); 
if(!nextobj.is(':visible')){ 
nextobj.slideDown('normal'); 
} 
return false; 
} 
}); 
}); 
</script> 
</html>

js css 实现遮罩层覆盖其他页面元素附图

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