Hi James. This is an issue of styles (that is, using the same styles on the forum pages as on the rest of the site), so I've moved this to the CSS forum.
It may not be too easy, though, as the forum doesn't have the same page structure as the site. Now would be a good time to consider how you want the forum to appear before playing with the styles. For example, do you want to carry over the menu etc? You will probably have to make quite a few compromises.