https://www.techradar.com/news/youtube-dark-mode-begins-rolling-out-to-android-users

After YouTube introduced a dark mode to its desktop site last year and migrated the feature to iOS in March this year, it’s finally starting to arrive for Android users.

The alternative theme exchanges YouTube’s white backgrounds and menus for a deep grey, aiming to alleviate the eye strain associated with brighter light when viewing in a darker room or at nighttime.