Some ideas about how @--import and @--export could be used to pass CSS objects between files

import-export.css

/* Export individual rules from a stylesheet */
@--export a {}
@--export b {}
@--export c {}

/* Define a list of rules as a default export for the stylesheet  */
@--export {
  d {}
  e {}
  f {}
}

/* Name an exported list of rules */
@--export named-list {
  g {}
  h {}
  i {}
}

/* Import a stylesheet's default export only */
@--import 'stylesheet.css';
@--import url(stylesheet.css);

/* Import exported objects by selector and/or exported name */
@--import (a, b, c) from 'stylesheet.css';
@--import (buttons, badges) from url(framework.css);