How To Enable YouTube's Dark Mode and New Look ?
Step 1: Go to the link below
Step 2: Click on Button "Try It Now".
you will get YouTube's New Look.
How to Enable YouTube's Dark Mode?
After you done enabling youtube's new look, Follow the steps below.
Step 1: Click on Your Profile.
Step 2: Click on "Dark Theme"
Step 3: Click on little slider to Activate Dark Theme.
It's done.