Need background size to increase when resized

When my site, tiny-picture.com, is resized in a browser, everything but the background resizes. I would like the background to resize in proportion to everything else.

I know there are a lot of how to’s out there and this subject comes up a lot, but I’ve spent the day trying several solutions, and can’t seem to make anything work.

Currently, the background is in the style.css body tag:

body {
	background-image:
	url(images/background.png);
	background-repeat: repeat-y;
	background-position: center top;
	position: relative;
}

My whole style.css is at http://pastebin.com/m6dUanqZ

Please help!