Jquery validation and styling the error message

Jquery validation and styling the error message

I would like to change the css used to style the error messages for jquery validation. I know i could create my own 

label.error {
  .....
}

but i really don't want to do that. We are already using a multipe css styles from an external library we are referencing for all our error messages. Sure i could copy/paste the css inside label.error {} but that would be a pain if the external stylesheets ever change. Please note we are not using Less or SASS (don't know if they make it easier) and don't plan on using them in the foreseeable future.