Theme states
One of the advantages of Drupal is the ability to have multiple themes available to use at any time. However, it is important to differentiate among installed, uninstalled, and default. We can consider these as the theme's states.
Installed themes
Installed themes are always located in the Installed themes
section of the Appearance admin and are available for Drupal to use for either the frontend or backend of the CMS. However, there can only be one theme set as the default at any given time. We can see a list of installed themes, as shown in the following screenshot:
Uninstalled themes
Uninstalled themes are themes that Drupal is aware of within the core themes
folder or the custom themes
folder, but have not been placed into an installed state. One or multiple themes can be present at any time within the Uninstalled theme
section, as shown in the following screenshot:
Default theme
It's important to remember that the default theme is always the current theme being displayed to users...