I'm not really sure what you are getting at. The css that controls the look of the menus has been mentioned here a couple of times now. Are you trying to add images or change things in this css that are not working for you? These are the rules that you should be adjusting to customize the look and feel of the side nav. Your other questions seem to all be geared toward what files and css control the look and feel of the menu so giving you the specific css file names and styles that control this should answer those questions.
Please post back if you have any specific questions that are not addressed by making use of the specified css to make edits to the look and feel. I will gladly help you with what I can but I'm not sure what you are looking for that has not been covered.