Twenty Eleven Fluid Design?

The Twenty Eleven theme must be a fluid design. It’s set to 1000px wide but it must have a set margin for the sides, which makes it shrink. I’m having to use an image instead of header text because customer wants the name to be in an unusual font style.

On a wider screen monitor all is well, but when I go to a 1024 wide monitor it throws everything off.

How can I eliminate the side margins? Where specifically in the style.css would I make this change?

Thanks