I'm editing message_user_info.css (from the route that shows both message_user_info and its .css companion), and even after I click "Save all Changes," the red dot that indicates you've changed something in the template seems to stay there.
If you have trailing white space, that can happen. More significantly, it can reflect that the value that you would get if you refreshed is different. This can happen for normal--or at least notable--reasons.