I noticed while using the jQuery UI Progressbar 1.8.7 that there was some extra space at the bottom of the progress bar. Turns out there was a bug in the jQueryUI/aristo/jquery-ui.css file, and adding a white background fixed the problem.
.ui-progressbar { height: 12px; text-align: left; background: url(images/progress_bar.gif) 0 -14px repeat-x; }
should be
.ui-progressbar { height: 12px; text-align: left; background: url(images/progress_bar.gif) 0 -14px repeat-x #ffffff; }