How to enable Gnome desktop dark theme on Ubuntu 20.04 Focal Fossa Linux - LinuxConfig.org

The objective of this artcile is show how to switch GNOME theme from light to dark on Ubuntu 20.04 Focal Fossa Linux.
This is a companion discussion topic for the original entry at https://linuxconfig.org/how-to-enable-gnome-desktop-dark-theme-on-ubuntu-20-04-focal-fossa-linux