title: jQuery css background-position animation
body: <p><br>
  I've got a strange problem with jQuery and CSS; it seems a jQuery bug; I've tried to search around but infos are ugly.<br>
  There's a large photo as background of the body; when I click on a button I wish to obtain a simple jQuery animation of the background, from "bottom" position to "50%" position.<br>
  Well, if I set <code>$("body").css("background-position", "center 50%");</code> it works but if I try tu use <code>animate()</code> jQuery function it doesn't works anymore.<br>
  So is it possible to have this effect in some way?<br>
  Thank you so much in advance.  </p>