I can't get that method to work myself. It may be possible,
but we'd have to guess at the syntax and tweak it until it worked.
However, I tried the original solution, and it works. I
created a 120x120px smiley face and put it near the upper-left
corner of a 1000x4000 white image, exported it as a GIF, and used
it as the background. It repeats, but I have to make the nav pane
extremely wide to see it repeat horizontally. (To eliminate this
problem, you could make the image 3000 or 4000px wide.) The image
is only 5KB in size.
Give that a try and see if it gives the effect you
want.