pabru
commented
6 years ago That's already supported.
- If your computer is a tower/desktop PC or a server, simply pull out the power plug while the computer is running.
- If your device is a tablet, phone or a laptop, simply hold the power button continuously until the screen turns dark.
It's not a very well-documented feature, but it's there. I hope that helps. There's a workaround that includes connecting a live EtherKiller cable (if your device has an Ethernet port), but obviously that's only for use in emergency situations.
Even Windows and Paint.NET have a dark theme nowadays.