Modify/Re-sizing footer

Hello,

I am using the Twenty-Thirteen theme. Basically, I want to change the footer width to make it smaller. I would like the footer to have the same width than the content area (1040px). I also want the top of the footer to touch the bottom of the content area.

I have managed to re-size the width of my footer using the code below.

#footer, #colophon {
max-width: 1040px;
}

Also, for information, I put a background picture on my pages. My problem is that The background picture stops at the top of the footer instead of going all the way down behind the footer and I am seeing a white background on the left and right side of the footer instead.

My question is, how can I manage to remove that white or extend the background picture all the way down behind the footer?

Thank you,