How do I make my footer background full screen? (HTML / CSS site)

How do I make my footer background full screen? (HTML / CSS site)

I've been trying to solve this for a couple of hours, but I haven't found
a good solution in this forum.
So, how do I make the footer background here stretch all the way to the
left and right, the way my header does?
I want the text to remain in four columns in the center of the screen with
its current width (950px), but the background to fill the viewer's screen,
whichever width that may be.
Thanks.
Maria