Well, How to Active Viber Dark Mode?
Once you open the app you will notice a notification at the bottom of the chat list. “Dark Mode” can also be activated by going to the “More” tab> Settings> Appearance.
If it still does not appear as an option, make sure you have the latest version of the app installed.
Walk on the dark side 🌃 Check out our new dark mode theme on Android! Save battery 🔋, protect your eyes 🙄, and keep the room dark when other people are trying to sleep.
— Viber (@Viber) March 5, 2019