I want a layer to pop-up on my site when user clicks a link, say "my favorites". Reference: Sitepoint Marketplace's "My Shortlist"

Here the parent div for this purpose is as follows

 border: 0px;
 padding: 0px;
 margin: 0px;
 width: 100%;
 height: 100%;
 position: absolute;
 background-color: #000000;
 opacity: 0.5;
 filter: Alpha(opacity:50);
 z-index: 500;
here its good, it covers 100% of browser window, when user scrolls i want the rest of the page to be like in Sitepoint Marketplace's "My Shortlist".

I guess sitepoint example i mentioned is enough to understand what I'm going for.

Thanks in advance.