According to the information, YouTube Music is now getting a new designs. At the top it identifies where the current song is “Playing from.” (Liked, playlist, radio or artist page). To the right is the relocated Cast button, which was previously in the interface when you clicked on the cover art.
There is now a more rounded corners, and the song title is aligned on the left edge. The “three dots” button is now more accessible, and the “Dislike” button is hidden there as well.
The play/pause button now has a white background and is no longer colored by the cover color.