Create A Forum - Support Forums

I'm trying out this forum to see if I can create a desireable layout. I changed the themes background, added a 2 part custom header but I'd like to lay a solid background underneath my headers & forums body section & leave the page background with about only 10% showing on the left & right, can't figure out what part of the theme css I should play with. Also I have my own chatbox I'd like to add & made to insert into blogs & sites like this, doesn't require any css but it won't load into the header template with my other header sections, I get an error message, don't have that trouble anywhere else tho. Any help would be much appreciated. Oh & if you want to see what I got so far, I'm @ http://hotrockcentral.createaforum.com thx