Dark Mode is a feature which inverses your device display so the bright white background becomes dark and the text light. Changing the contrast to be easier on the eyes by reducing the amount of harmful blue light. Studies have shown blue light is attributed to keeping one awake contributing to higher rates of insomnia among computer and mobile users.
There are a few ways to achieve this : In the OS like MacOS, Windows10 or Chrome, an App like YouTube, Microsoft Office, etc or as an Add-On like in the Chrome or Firefox browsers.
In the App eg. Microsoft Office has a “Dark Mode” in the “Options” section, under “Personalize your copy of Microsoft Office” ; Office Theme: “DARK GRAY”. There is also Black and whit, etc.
Windows 10 has this capability under the “Display Options” setting, and just release MacOS.
The Chrome browser achieves this with an ADD-ON.
DarkMode is a great way to relax your eyes and is particularly useful in bright sunlight or night time. Check it Out you might prefer these mode vs the brigh white background,