Doesn't seem to work for me. I uploaded my user group banners to a directory I created called userbanners and pointed the CSS to them by going to
https://codinghelp.site/userbanners/image.png (pointing to each image)
Then I updated the roles in the settings by using the custom CSS class name I created which was adminBadge (for one of them) and nothing updates.
I even tried adding the CSS to the usernameCSS section and that did not work.