Modifying Kubrick Default BG

http://sarahreynolds.net/wordpress/

I’m trying to break down the Kubrick theme and build it back up, a little customized. I’ve increased the width of my page but I cannot figure out how to modify the background of the content. (It is currently too narrow, and has a border I don’t want.) I’d like to just axe the b.g. and start with a solid color–where do I find this in the CSS?

Thanks in advance for help!