The dark ones themes they come and go these days. For example, Android, iOS and Windows now also have a dark mode, while the majority of new apps that are released also have a dark look.
As can be seen, Google is also preparing a dark mode for the machine search, in an effort to provide more consistency to Appliances which dark theme mode is enabled.
Thus, the company recently started testing dark mode in Google Search on Android devices.
The dark feature on Google.com is only available for the browser Google Chrome and comes with an experimental flag for now. Logically after the tests, it will be released for all mobile devices.
It remains to be seen if the dark mode of Google.com will reach the desktops at some point. Of course, it will take some time for the tests to be completed, but apparently everything will darken sooner or later.