/* main styling of layout messages */
div.jGrowl div.jGrowl-notification, div.jGrowl div.jGrowl-closer {
  background:#000;
  color:#fff;
}

/* styling of error messages in particular */
div.jGrowl div.jGrowl-notification.jgrowl-error, div.jGrowl div.jGrowl-closer.jgrowl-error {
  background:red;
  color:#fff;
}