Best way to account for overlapping <body> background [#1292592]

My site uses a background on which elements must be positioned on top of. By default, admin_menu seems to push down the content of the site, but not the body background, so it breaks the theme. I can turn off the 20px margin in admin_menu settings, but then the admin menu lays on top of my top menu, rendering it inaccessible.

I am developing the theme, so I can use whatever method is needed, but what is the best way to handle body background images that need to be positioned correctly at the top of the page? I supposed I could add another div inside body just to hold my background, but that doesn't seem very clean.