lib/transforms/html.styleTransforms.js
function fileToReadable (file) {
  class VFileReadable extends stream.Readable {
    _read () {
      this.push(file);
      this.push(null);
    }
  }
  return new VFileReadable({ objectMode: true });
}
function fileToReadable (file) {
  class VFileReadable extends stream.Readable {
    _read () {
      this.push(file);
      this.push(null);
    }
  }
  return new VFileReadable({ objectMode: true });
}
this module fileToReadable (file: VFile) => stream.Readable