BG image position is not displaying as expected

Hello WPMU dev community,

I am sure that this is a simple question for most of you, but I am still a novice when it comes to code.

I am working on a site using the ShapeShifter2 theme from ThemeForest. I can usually figure out how to customize most everything within themes, but the background image position on this one has me stumped.

I have set the background image position to "center top", but the image is displaying as if it is "left top". There are several CSS files for this theme, and I am not sure if there are multiple instances that need to be updated. Also, the image is large -- 2200 x 1460 and is meant to bleed off the edges of the browser window -- bleed on the left, right and bottom, that is.

I would appreciate if someone would take a moment to look at this and hopefully tell me the one small thing I've missed here...

(The site is in the very beginning stages of development... I got stuck on the BG image and can't seem to continue with anything else until I figure this out!)