Email styling and CSS is a whole specialty I don’t have or care to learn. There are services designed to help test this stuff and it’s a pain. I also don’t use this feature, so I just don’t have the requisite knowledge. Sorry!
No need to apologize. I’m grateful for yours and @mandaris 's help getting things this far.
I don’t know CSS at all — email or otherwise.
I’m going to declare this “good enough for now” and move on. Maybe come back and work on it another day.
I’ve been involved in professional marketing and editorial newsletters, from a content rather than technical side, but I seem to recall talking to technical folks that Gmail is a special case and tough to design for.