It turns light colored websites into dark websites [1][2][3].

Here is an example: https://colinespinas.github.io/darken/

[1] https://support.apple.com/en-ca/HT208976

[2] https://css-tricks.com/dark-modes-with-css/

[3] https://developer.mozilla.org/en-US/docs/Web/CSS/@media/pref...