Thanks for pointing out a mistake I was making.
I entered this: #xxyyzz url(images/misc/image.gif) top center repeat-y
in the Background box of the Standard CSS Attributes of the Body section, and it works the way it was working the hard way. I was making it more complicated than it needed to be.
I'll see if I can figure out this wrapper stuff later. But for now, thanks for helping me see the mistake I was making.