Google is testing the dark theme on the search page again. It was last month that users last reported seeing a dark theme.
The dark theme of the most visited pages in the world follows your favorite Windows or macOS theme. If set to light, Google search will not change. If set to dark, a new dark theme will be displayed.
The dark theme makes the background very dark gray instead of completely black. The text has changed from black to white, but the link remains blue.
Google is still in A / B testing, so changes may not be available yet. When you do this, Google Search will display a message about the new dark theme and you can choose to enable it or continue as usual. I don’t know when the dark theme will be carried over to mobile browser searches.