function to convert your css string to downloadable file

cssStringToFileDownloader.css

cssStringToFileDownloader = function (cssString) {
  var blob = new Blob([cssString], { type: 'text/css' });
  var el = document.createElement('a');
  el.download = 'cssPaletteBundle.css';
  el.href = URL.createObjectURL(blob);
  el.dataset.downloadurl = ['text/css', el.download, el.href].join(':');
  el.style.display = 'none';
  document.body.appendChild(el);
  el.click();
  document.body.removeChild(el);
  setTimeout(function () { URL.revokeObjectURL(el.href); }, 1500);
};

/* cssStringToFileDownloader('body{padding:12px;}') */