LUbuntu 20.04 LTS “Focal Fossa” is shipped with a default dark theme. You can activate the dark version of the standard Ubuntu Yaru theme and get the dark GNOME desktop with just a few clicks. This is how you do it.
First, click the system menu button in the panel in the upper right corner of the GNOME Ubuntu desktop and select “Settings.”
You can also click the “Show Applications” button in the lower left corner of your screen, search for the “Settings” application, and launch it from there.
Click the “Appearance” category in the Settings application.
By default, Ubuntu uses the “Standard” window color theme with a dark toolbar and lightweight content panel. To activate the dark mode of Ubuntu, click “Dark” instead.
To use light mode without the dark toolbar, click “Light” instead.
Your changes will take effect immediately. You can now close the window.
Note that this will not change the Ubuntu interface panel to dark mode. For example, when you click on the menu button in the upper right corner of your screen, I will see that it has a bright background even when dark mode is activated.
To change the panel theme, you must install the GNOME Shell extension. OH, GOD! Ubuntu! has a guide that will guide you through the process of installing the gnome-shell-extensions package, activating the “User Theme” extension, and switching the “Shell” theme to “Yaru-dark.”