Extend CSS of a Drupal 8 Contrib Module

# These parts extend an existing module's CSS, allowing you to build on top of it.

# THEME.libraries.yml
/**
 * In this example, we're extending the eu_cookie_compliance library.
 * This part declares the new library you'll be creating to extend the existing
 * CSS.
 */
eu_cookie_compliance:
  version: 1.x
  css:
    component:
      css/contrib-overrides/eu_cookie_compliance/eu_cookie_compliance.css: {}
      
# THEME.info.yml
/**
 * In this example, we're extending the eu_cookie_compliance library.
 * This part does the extending of the library you'll be creating to extend the existing
 * CSS.
 * 
 * In this section: eu_cookie_compliance/eu_cookie_compliance, the first part before the forward slash is the
 * name of the module, the naming after the slash is what it is declared as in the module's libraries.yml file. 
 * As such, the module's library declaration might not be obvious, so look into that yml file to learn what it is.
 */
libraries-extend:
  eu_cookie_compliance/eu_cookie_compliance:
    - THEME/eu_cookie_compliance