UBB.threads PHP Forum Software Community Forums UBB.threads 6 Version 6 Support Putting a background image for whole board

Hi all
I've been playing with the CSS editor and have set the colour scheme to one I am happy with.
However, i'm not happy with the plain white background (all the blank space around the boards etc).

Where /which template/file do i need to modify to include a background image, so that all the whitespace is replaced?

All help appreciated (as usual).

Thanks