Full page issues with white background

Using iAdvanced frame and full page template, I want to clean up how the forums look but am sort of a CSS newb.

Click Forum to take a look.

I want to remove the white entirely, and the only place I think I can is in the post.css file and remove the margins.  But it also removes the margins from the actual articles and makes it look horrible.

Is there any way to create a specific class for full page layout or something that doesn’t use that white background for my forums, but still keeps it for the news posts?