js+css realizes the masked pop-up layer in the center (scrolling with the browser window scroll bar)
Copy the code code as follows:
<!doctype html>
<head>
<meta charset="utf-8" />
<title></title>
<style type="text/css">
*{}{margin:0;padding:0;}
html{}{_background:url(about:blank);} /**//* Prevent flashing in IE6, replace empty files with about:blank, reduce requests*/
body{}{background:#fff; font: 12px/1.5 Tahoma,Geneva, //5b8b//4f53, sans-serif; height:100%;}
.wrap{}{height:980px; padding-top:20px;text-align:center;}
p{}{font-size:14px;text-align:center;line-height:24px;}
/**//** Mask layer**/
#masklayer{}{
background:#000;
display:none;
filter:alpha(opacity = 50);
opacity:0.5;
top:0;
left:0;
height:100%;
width:100%;
z-index:999;
position:fixed;
_position:absolute;
_left: expression(documentElement.scrollLeft + documentElement.clientWidth - this.offsetWidth);
_top: expression(documentElement.scrollTop + documentElement.clientHeight - this.offsetHeight);
}
/**//** Pop-up layer**/
#popup{}{
display:none;
width:300px;
z-index:1000;
left:50%;
top:50%;
position:fixed!important;
margin-left:-150px !important;
_position:absolute;
_top:expression(eval(document.compatMode && document.compatMode=='CSS1Compat')?
documentElement.scrollTop + (document.documentElement.clientHeight - this.offsetHeight)/2: /**//*IE6*/
document.body.scrollTop + (document.body.clientHeight - this.clientHeight)/2); /**//*IE5 IE5.5*/
}
.content{}{background:#f3f3f3;border:1px solid #999;}
.content h3{}{background:#a0a0a0;color:#fff;font-size:14px;height:32px;line-height:32px; padding-left:5px;}
#clickbtn{}{margin-top:20px;}
</style>
</head>
<body>
<div>
<p>
I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text
<br />
I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text
<br />
I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text
<br />
I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text
<br />
I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text I am the main text
</p>
<input type="button" id="clickbtn" value="clike me" />
</div>
<div id="masklayer"></div>
<div id="popup">
<div>
<h3> Is the popup layer centered? </h3>
<p>Center, center, center, center, center, center</p>
<p>Center, center, center, center, center</p>
<p>Center, center, center, center</p>
<p>Center, center, center</p>
</div>
</div>
<script type="text/javascript">
(function(masklayer){
var clickbtn = document.getElementById('clickbtn');
clickbtn.onclick = function(){
var popup = document.getElementById('popup');
masklayer.style.display='block';
popup.style.display ='block';
var h = popup.clientHeight;
with(popup.style){
marginTop = -h/2+'px';
}
}
})(document.getElementById('masklayer'))
</script>
</body>
</html>