Dark mode/light mode

[fossfreedom]

Think about introducing a light / dark mode depending upon which type of theme is installed

https://css-tricks.com/a-complete-guide-to-dark-mode-on-the-web/

e.g. if theme has the name "dark" in it then could we assume dark mode automatically? Some themes such as "arc-darker" is not actually dark - arc-dark is though.

Users should have the ability to toggle automatic dark-mode.