I've given up on my Yahoo mail.
For some time, every time I go to log in I have been urged to choose a theme (why?). I discovered that clicking on 'Not now' meant until next time I tried to log in, and even choosing one of their bloody themes and saving it didn't work since I was greeted by the same popup asking me to choose a theme next time
Even if I am really quick in clicking on a new mail, that popup appears and gives itself priority over my opening the mail.
Waste of time now.