I know that's a goofy Subject; I couldn't even think of what to Search for.
I'm trying to configure a very simple layout at http://www.websites10dollars.net/
I've set the container width to 750px and trimmed out a lot of stuff... using the settings page.
But look at the screen capture to see how the gray bars are coming in too far both at the left and even worse at the right.
I can't find anything in the settings that seems related to the background outside the container... or whatever that is.