Adding a background image to a widget

I’m very much a html and css newbie.

Is it possible to set up a text widget so it has a background image with formatted text over the top?

I tried:
<div style="background-image: url(http://site.com/path/myimage.jpg)"></div>
but it doesn’t show.

This does display the picture so the link must be correct:
<img src="http://site.com/path/myimage.jpg" />