2022: Can you please reconsider this?
2021: Hi :) Dark Theme is only Youtube's setting anymore. (top right menu of on www.youtube.com!) - We might rename it to be clear "Dark(from youtube)". (The other themes, including black/OLED are made by us) (you could also use our button to remove Youtube's cookie).
You might easily notice the addon runs 100% offline & does nothing (until you tell it to edit your youtube styles or playback). And that the code is open & pure. Please review our volunteer initiative: https://github.com/code4charity/Youtube-extension. Please revise the star rating.
Many smiles!