User-1174608757 posted
Hi tadbirgaran,
According to your description, Could you please the detail about code in your css file?
TypeError: css.style.backgroundImage is undefined -- in WebResource.axd
This error means the program couldn't find the background image , so I think may be the image url is not correct? I hope you could give me more information, it will help us to solve your problem quickly.
Best Regards
Wei Zhang