Solid background color

I'm working on a draft site for a non-profit that I'll move a little later. (Thus the inconsistency between website name and content.)

I would like to have a solid blue box around the whole site, and I can't figure out how to do it. I've added the border, but that's not what I'm really looking for.

http://myseattleschools.org/

There are huge white spaces on the left and right that I want to be blue. I know this is a silly question, but I'm completely lost!