Drupal uses Tables for its Forums. Tables don’t get a lot of respect in this day and age but they are still useful for many things. And Forum/Bulletin posting sites are one of them.
So I am trying to make the tables fit on a 320px width screen. Not easy. After playing around with several different CSS settings, I discovered that using
table-layout: fixed;
really seemed to help me. I had been shrinking the fonts to make the tables fit, with mixed results. Using the fixed setting helped.