Over the last couple of days, the layout of the site has changed drastically and in small ways after that. What's happening? Was there an announcement? They are convenient changes, anyway, but was this supposed to be announced?
There are ongoing changes, as documented in New post summary designs on site home pages and greatest hits now; everywhere else eventually to make all sites on the network more mobile-friendly.
As it was not well received, the community over there has requested many changes, which have been rapidly deployed. Hopefully things will settle soon.