Anyone got background images for DIVs working? The "background-image(url...)" thing in CSS?

I just don't get it. The background-image(url...) construct in a CSS does *not* display the image for me (neither in a web app, nor on a web page I load directly from the web). - I'm not sure, however, if the CSS property is completely ignored: In one case I see the background becoming blue when the image is mainly blue... in some cases, it's just like there's nothing at all.

So is it something in the CSS S40 is picky about? Or does it only accept certain image formats as backgrounds? Is there any working example that I could have a look at?