Our main focus for the Domicile theme is restyling Drupal's markup with CSS. Although it is tempting to put all of your CSS into a single file, things can quickly grow out of control. In our theme we'll break our CSS into smaller stub files to make the theme easier to maintain using the file naming conventions for Drupal 8.By the end of this lesson you will be able to incorporate CSS files into your theme via the theme's .info file.
Check your version
This video covers a topic in Drupal 7 which may or may not be the version you're using. We're keeping this tutorial online as a courtesy to users of Drupal 7, but we consider it archived.