I have the gadget called "Add an  link for the lead section of a page" enabled on en.WP, and have done for as long as I can remember. Just in the last couple of days, probably since Thursday, the "edit" link for the lead section shows in a different font from the "edit" links for all of the other sections on the page. This is happening in every namespace, as far as I can tell.
Another editor writes: I see serif in Vector but sans-serif in Cologne Blue, Modern and MonoBook. The gadget code is in MediaWiki:Gadget-edittop.js and MediaWiki:Gadget-edittop.css.
Another editor confirms: Not just you, this also changed for me in the last couple of days.
The lead section's edit link should show in the same font and size as the rest of the edit links on the page.