node_modules/stylehacks/src/isMixin.js

/**
 * @param {import('postcss').Rule} node
 * @return {boolean}
 */
function isMixin(node) {
  const { selector } = node;

  // If the selector ends with a ':' it is likely a part of a custom mixin.
  if (!selector || selector[selector.length - 1] === ':') {
    return true;
  }
  return false;
}

export default isMixin;