I use a pretty widely used 'css-rounded-rectangle' routine: Nifty Corners Cube (
http://www.html.it/articoli/niftycube/index.html).
But it breaks in OW (it works in Safari, Firefox, IE etc) because, apparently, OW doesn't handle css block padding in the same way as the other browsers. If you try some of the examples on the page (above) you'll see the problem. I have tried various 'work-arounds' with no luck.