Using the OS to invert the whole screen can easily be put within easy reach by keystroke or notification-area-button on Android, iOS, Windows, Mac, and Ubuntu.

Using the OS to invert the whole screen can easily be put within easy reach by keystroke or notification-area-button on Android, iOS, Windows, Mac, and Ubuntu. It doesn't require installing any new software (it's usually somewhere in "accessibility"), and, most importantly, it's consistent. When you have a "dark mode" for one site or app, it fights with the surrounding browser chrome bring light, and switching to other apps is jarring. And when you try to enable a dark UI theme in the OS, inevitably there will be elements that missed the restyling, and so retain black-on-white, or even worse, are now black-on-black. I get that a "dark mode", done properly, requires more than just inverting colors, but this consistency is really nice.