The top bar on Area 51 seems to be malformed:
For a while now, Area 51 has been using an older version of the top bar on Stack Exchange sites, that better conforms with its 2011 design. However, it seems the assets for that old top bar were removed, meaning that the bar now looks malformed. The top links ("Stack Exchange", "Inbox", and "Reputation and badges") still work and show the popups in their previous spots, but they don't mesh with anything and just appear detached.
Also, the links appear with very little contrast, which makes an accessibility issue.