govcms-2.x-dev/themes/custom/govcms_install/govcms_install.libraries.yml

maintenance-page:
  version: VERSION
  css:
    theme:
      css/theme/maintenance-page.css: {}
  dependencies:
    - system/maintenance
    - seven/global-styling

install-page:
  version: VERSION
  css:
    theme:
      css/theme/install-page.css: {}
  dependencies:
    - seven/maintenance-page