YouTube has come up with several relatively fundamental design changes that can not be noticed. First of all, there is a new logo with a new font and play button. Changes have also been made to a mobile app that can play video in portrait mode, you can set the playback speed and double tap.
And last but not least, a new web version that has been available for a long time. If you are not active yet, you can turn it on at youtube.com/new. It’s definitely a sharper design, it sinks red in color and gets more bright colors - white and gray. This may not suit everyone, especially at night. There is also the option to switch to Dark Theme.