User Can Choose Background Image

[smartkidbk5]

Well I am trying to make it where a user can choose their own background image.
I have a profile field set up where the user can enter a link to the image.

Then in the vbulletin.css file, instead of stylevar, I just did this:

html {
	background:rgb(0, 0, 0) url({vb:raw post.field17}) no-repeat  fixed center top;
}

But for some reason it isnt working. Is the variable wrong? Or is there another way to do this?

Thanks.