Other answers seem to skip important info. If you have the same code from your question in your subtheme.libraries.yml file, but it isn't showing up, you still need to add that library to your subtheme.info.yml file
subtheme.info.yml
name: Subtheme Name
type: theme
description: 'A theme description.'
core_version_requirement: ^8 || ^9
base theme: bartik
libraries:
- subthemename/global-styling
- subthemename/font-awesome
- subthemename/bootstrap
subtheme.libraries.yml
global-styling:
css:
theme:
css/styles.css: {}
js:
js/scripts.js: {}
font-awesome:
remote: https://fortawesome.github.io/Font-Awesome/
version: 4.5.0
license:
name: MIT
url: https://fortawesome.github.io/Font-Awesome/license/
gpl-compatible: true
css:
theme:
https://maxcdn.bootstrapcdn.com/font-awesome/4.5.0/css/font-awesome.min.css: { type: external, minified: true }
bootstrap:
remote: https://getbootstrap.com/docs/5.1/
version: 5.1
license:
name: MIT
url: https://getbootstrap.com/docs/5.1/about/license/
gpl-compatible: true
css:
theme:
https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css: { type: external, minified: true }
js:
https://cdn.jsdelivr.net/npm/[email protected]/dist/js/bootstrap.bundle.min.js: { type: external, minified: true }
Put another way, you first need to specify the library names in your info.yml file then define them in your libraries.yml file.
