How to Enable Dark Gnome Shell Menus, Calendar in Ubuntu 20.04

Ubuntu 20.04 introduces new dark mode in the Settings utility. It is however not full dark when you turn it on in Gnome Shell. System tray menu, top-bar calendar, notification popups, and desktop context menu are not dark but always light when you switching between light, dark, and standard modes. Enable Full Dark Theme in Ubuntu 20.04: 1.) First install user themes Gnome Shell extension. It was able to install the extension simply via Ubuntu Software when I was in Ubuntu 18.04. Ubuntu 20.04 however shows me “No Application Found”…