Custom base CSS not compiled or referenced

Problem/Motivation

When adding custom CSS to the base.pcss file, these custom CSS are not compiled and exposed to the final theme.

Steps to reproduce

- edit base.pcss and add custom CSS
- rebuild the CSS using npm run build
- clear cache on web site
- Custom CSS is not applied

Proposed resolution

- rename base.pcss to base.pcss.css in order for the build process to capture the CSS file
- update the theme libraries YML file to reference dist/css/base/base.css

Remaining tasks

none

User interface changes

none

API changes

none

Data model changes

none