my simple rollup-plugin-postcss (updated)

postcss.js

import { createFilter } from 'rollup-pluginutils';
import { writeFile } from 'fs';
import postcssrc from 'postcss-load-config';
import postcss from 'postcss';

export default (options = {}) => {
  if (!options.include) options.include = '**/*.css';

  const filter = createFilter(options.include, options.exclude);

  return {
    name: 'rollup-plugin-postcss',

    async transform(source, id) {
      if (!filter(id)) return;

      const filename = id.split('\\').pop().split('.').shift();
      const { plugins, options } = await postcssrc();
      const { css } = await postcss(plugins).process(source, { ...options, from: id, to: `public/${filename}.css` });

      writeFile(`public/${filename}.css`, css, () => true);

      return {
        code: '',
        map: null,
      };
    },
  };
};