First off (I don't actually care but others will remind you of it): If you are posting a code sample, please use the code snippet button in the toolbar. It preserves indentation in your code and makes it easier to read. It's the first button on the left of the toolbar, so you can't miss it.
Now to your problem:
you used the shorthand "background" property without naming every value, maybe that could be the problem.
Other than that you could try to set "background-size" to "100% 100%". It will probably skew your picture, but maybe it's worth a try.
I hope this helped.