Sass stylesheets (in SCSS format) are loaded in alphabetical order. Prefix the stylesheets with letters to control this order.
Styles are then minified on build to css/styles.css.
If you're not familiar with Sass, in its SCSS format it is a superset of CSS, meaning you can use any valid CSS within the Sass files even if you don't want to learn anything about Sass. For more information, see https://sass-lang.com/documentation