Themes are made up of different types of files; name a few Drupal-specific file types.

=> THEMENAME* dependent on purpose using.

What is the one file required of every theme?

=> THEMENAME.info.yml

What is the benefit of placing your custom theme into the /themes/custom directory instead of just /themes?

=> In /themes folder will sub-dividing

• themes/contrib/ for all themes downloaded from drupal.org
• themes/custom/ for your own custom themes

With this divide, we will sure know that this theme is downloaded from drupal.org (will update if need in the future) or own custom theme

Other than /themes, where does Drupal look for non-core themes?

=> sites/example.com/themes