Have you looked at apps like f.lux - https://justgetflux.com/ - or Twilight (Android) - https://play.google.com/store/apps/details?id=com.urbandroid.lux&hl=en_US&gl=US ? There's plenty of competitors if those doesn't suit your OS.

You get automatic dimming at night, or you can just turn it on all the time and adjust the blue/red/brightness to your liking. I haven't felt the need for "Dark Mode" anything, since these apps will cover all apps/websites.