How to create new CSS-enabled content area within existing "Container" area

Hi!

Thanks in advance for your help.

I need to create a CSS-enabled content area within the existing #container area. Basically, I'd like for the background image I'm using to extend the entire width and length of the page and to able to "layer" the #container area on top of it. The specific effect I am going for is that of a piece of paper (#container area) on top of a desk (body/background area).

What would be the easiest and most compliant way to do this?

Thanks again!