How do I enable dark mode / light mode?

Switchboard will change between light mode and dark mode based on your computer's settings. Check out these articles on changing your computer's settings:

Mac- https://support.apple.com/en-us/HT208976

Windows- https://blogs.windows.com/windowsexperience/2016/08/08/windows-10-tip-personalize-your-pc-by-enabling-the-dark-theme/