I've had the same issue with gmail. The back and reply buttons are nearly identical, the reply one is just a bit curvier. I don't know why google has a reputation for good UI's, most of the ones I've used have varied from decent to awful.
YouTube's ContentID UI deserves a special mention, it's not just awful, it's actively sabotaging people questioning ContentID strikes (90% of which are fraud.)
Or try the new Google Hangouts desktop "app". (Not really an app any longer-- now only the Chrome add-in is available.) It's hilariously awful. It's almost as if they're trying to sabotage their own product. Don't take my work for it, read literally any of the reviews on their own app site:
https://chrome.google.com/webstore/detail/google-hangouts/nc...
Sorry. I could rant about how terrible Google's UI/UX is for days.