That site actually does some other changes. They have one div for the whole userinfo. Then inside that, a top image, then a div with all the text userinfo text and a background image is used here repeated in the y direction, then a bottom image. So, that is how they get it to expand to any size. So, you would need to modify your postbit_legacy template in order to achieve what they have done.
HTML Code:
<div class="userinfo">
<top image centered>
<div class="newclass"> all stuff from div class userinfo now put into here </div>
<bottom image centered>
</div>
and then have a background image for .newclass