No other improvements are implemented in this update other than the new dark theme. However, other things that also worth noting on this update is its availability only for users of iOS operating system device.
This feature changes the number of colors in the YouTube user interface, eliminating the white background and replacing it with black color that is considered more cinematic impression.
YouTube calls this feature to be one of the most user-requested features to be presented on mobile apps, since it was launched on YouTube last year's site version.
To enable this feature, just tap the account icon, then access Settings, and then select "dark theme".