code: function addCssExtension(args, styleExts, extensions) {
    for (let x = 0, len = args.length; x < len; x++) {
      if (styleExts.includes(args[x])) {
        extensions.push('.' + args[x].slice(2));
      }
    }
  }
docs: Grabbing style extension from arguments and adding to
  full list of extensions