Changing background of main content

Hi, I’m using the Fusion template and am trying to change the background of the main content of the pages and posts. As you can see from my site http://www.askadamleague.com, I changed the background to an image. But I don’t want the text to float in space and I’d like to make a table or block of color behind the text. Can someone tell me how to do this? Is it done in the style.css or in one of the .php files? And where in the code do I insert the background-color? Thanks