css64.js

var css64Encode = function (string) {
  return $.base64Encode(string).
      replace(/\//g, '--_').
      replace(/\+/g, '-_').
      replace(/\=/g, '_');
};

var css64Decode = function (string) {
  return $.base64Decode(string.
    replace(/--_/g, '/').
    replace(/-_/g, '+').
    replace(/_/g, '='));
};