It looks like Google is testing a new dark mode for YouTube that isn't ready to go live for some reason. However, if you follow these steps then you can force it to be enabled on your desktop right now. . . 1. Open console 2. Paste: document.cookie="VISITOR_INFO1_LIVE=fPQ4jCL6EiE" 3. Reload 4. Click your avatar 5. Dark mode!