Walking into the theater for Eightythree Down at Under St. Mark’s is like going back in time. The eighties music provides a backdrop to the Duran Duran and Bowie posters, the VHS tapes on the bookshelves, and the level of electronic technology. The year is 1983, but it won’t be for long. Tonight is New Year’s Eve, and Martin thinks he is going to spend a quiet evening at home. The Horse Trade and Hard Sparks production of J. Stephen Brantley’s play is overdone at times, but is still a nice piece of theater.