Please show us what you put in the css, and how you edited it..   tis the only way we can troubleshoot it for you.

If you edit the css directly to add a backgorund image and save it , which is what you did when you added the background image..  you have to edit it again and edit the .windowbg area and add the code there.    When you did it at the top section and save it, that section doesnt know the changes you made earlier in the css.      You have to do one or the other -  can not switch between them.