This extension installs a dark theme which makes Youtube black with the click of a button. Simply install this extension
to enable dark mode on Youtube.  Protect your eyes at night by changing the Youtube background color into black.

This application allows you to switch on /off Dark mode for Youtube (aka Night mode, dark theme). Give a little rest for your eyes (especially at the night time) and install this extension.

Once you install this extension, to switch dark mode on/off, what you need to do is click on the top left hand slider button on Youtube.com.