Ah, then I can understand the problem.
The current version of extra-menus has NO css included in the module. I suspect you are looking at old files that should have been deleted. They are wrong, and not used anywhere by kiwitrees code now. An extra-menus module folder should only contain two files, module.php and a help file (which will also be removed soon).
Copy your css for the images from the main colors theme /css/style.css file. Look at about line 1813.