Google seems to be rolling out a new User Interface for desktop search results. The new UI is different from the old in that it has a more rounded design (including the search bar), a sticky header, and a smaller logo.
Google started testing this interface in August, and more an more people have been noticing it lately. I am able to replicate it in different browsers on different desktop devices which usually indicates a rollout, although it is possible that Google is still running a very large test.
Google rolled out a rounded UI for mobile search in November 2017, and this new update helps them to close this gap between desktop and mobile UX.
Here is what the Google Search design looked like before the update: