A while back we showed off a little trick to enable YouTube's secret dark mode. Now, there's an official way to opt into the new look.
The new look isn't just about the dark mode. It's also a whole new design for YouTube. That means Google is applying the Material Design seen on its other platforms. In this case, the navigation buttons get moved around a little, so you'll do everything from the navigation bar on the left as opposed to both the navigation bar and the tabs at the top. Otherwise, things are pretty much the same as they were before, albeit a bit snappier to use.
All you need to do to enable the new mode is head to youtube.com/new, and then you can opt into the new design. Once there, click your profile icon (or the three line icon if you're not logged in), then click on Dark Theme to enable it. You can also click on Restore classic YouTube to return to the old look if you don't like the new design.