How does one customize the icon for item categories?  I see the Icon field under settings/categories, and tried inserting a path to a custom icon, filename of file uploaded to a few different directories, etc. but only end up with a blank category button. 

Right now theme expect font awesome tag.
If you want urls, you must update a theme bit.

Thanks.  I figured out from your response that the system allows font awesome characters.  Took me a bit to figure out the proper syntax though.  If anyone wants to change the images for the categories links, look up font awesome online.  The symbols have codes associated with them such as fa-car for a car image.  In OSClass under settings/categories, insert something like:

fa fa-car
in the icon field to change the image to a car.  Don't forget the extra fa in front of the image code you want to add.

@bkfly1
That's correct, thanks for feedback