Spry TabbedPanels Widget

Hi All,
I've been experimenting with the Spry Tabbed Panels Widget to produce a
navigation system for a site. It works pretty well except for my inability to
center the main Div container. I've manipulated the Spry CSS considerably to
produce the display I need, but have been unable to have any effect on the
centering. Should I be looking at changing the controlling Javascript? Can
anyone advise please?
The link is:
http://www.webpedlar.co.uk/spry_test/index.htm