Different CSS Classes For coupon-message

I'd like to see a CSS class added to coupon-message when a message is displayed indicating that a coupon is expired or invalid so that I can theme those messages in a different way than those which indicate a coupon has been added or removed from the cart. Currently, the coupon-message ID is always used regardless of whether the message is considered to be a successful addition or subtraction of a coupon, or an "error" (invalid or expired coupon).