Dark Theme for YouTube (Chrome, Firefox, Edge, and Opera) gives YouTube a customizable dark theme.
With Dark Theme for YouTube, you can alter most of the defined colors allowing you to customize YouTube to suit your taste, not to mention save your eyes from the default glaring white. It also allows you to apply your own CSS rules to the default theme, and it will enhance the native dark theme so it will be compatible with YouTube theme changes.
Dark Theme for YouTube will also permit you to set a schedule to enable or disable the dark theme at specific times of day or night. Perfect for those late-night MajorGeeks Youtube sessions!