I am constantly re-working Drupal's tabs to look a little bit more like a pile of bricks, and I've finally decided to stop reinventing the wheel and to document the CSS that makes them display more sanely. (Namely, if you have a narrow main column and a lot of tabs, they start disappearing into the ether over at the right).
I hope this snippet helps some other folks, too.
This fixes your default Drupal tabs by taking it from this:
UPDATE 2/8/2016 (my birthday!)
I still use this - and here it is in SASS. I took the advice to use ul.tabs, too. That way it doesn't also affect primary links.