Background not zooming like the main site with ctrl + mousehweel

[Azurafiles]

I have added a static background code to my website, which works, but how can I make the background zoom with the main website, without the background being more and more visable?

Try to zoom in on my site, and you will notice that the background gets to visible.
I need it to follow the main site when people zoom it:

http://www.aero-files.com/shop/