To build an FSCSS module like st-core. fscss , create a stylesheet of reusable @define mixins, expose a small public API, and compile/test it with the FSCSS CLI. st-core follows this pattern for design tokens, layout helpers, charts, stat cards, and progress bars.
Source: [Dev.to](https://dev.to/fscss/how-to-build-an-fscss-module-like-st-corefscss-1d6l)