sidebar overrun

I love the Oxygen theme, but I’m having a puzzling bug that I can’t seem to fix.

When I have widgets in either the primary or secondary sidebar, it seems as though the widget content is over-running the width of the widget.

I’ve screenshoted the two examples:
https://dl.dropbox.com/u/18646988/search%20bar%20overrun.png
https://dl.dropbox.com/u/18646988/widget%20overrun.png

And you can probably see it live at http://www.streathamlocal.co.uk/

I’ve tried everything in the CSS but can’t seem to fix it. Does anyone know how this can be fixed?