YouTube now officially has a setting to turn on dark theme on your desktop browsers.This apparently has been out for a few months so this is only for people who haven’t heard of the news yet. And it’s very easy to access as it sits right under your account actions drop-down on the top right. So the days of using YouTube dark theme extensions could be over. Try it out if you haven’t already.
The dark theme works throughout the YouTube site except the settings page. It’s not often you visit the settings page anyway.
The features works on most latest browser (tested on Firefox and Chrome) but may not work on some forks like Pale Moon. The dark theme settings are save on browser and not your account but it also works without logging in so you can enjoy the new dark theme on your private browsing as well.