In the macOS Mojave update released in the autumn of 2018 a Dark Mode was added. While in many people’s opinions it is a welcome visual enhancement it was also added to aid concentration and to ease computer use for those who work into the evening and night.
This feature is easy to turn off and on, the steps are below.
Select the System Preferences icon (img. 1).
Choose the General icon (img. 2).
You can now toggle between Light and Dark (img. 3).
Many applications that you run will automatically switch between Light and Dark Mode but some may require you to switch in the application’s preferences.