Thanks again Conor but that doesn't meet my needs.
Yes, you could replicate those styles to style the inner messages of the form but the attachment of behaviour to close the message would still need to be done.
I'd rather not have to replicate and shoe-horn the styles to look the same but rather just hide the messages and be informed through a callback as to when I can read that message and delegate showing it via our existing module.
Additionally, upon success of the form submission, I'd like to send a custom event to Google Analytics to track that asynchronous goal - again, to keep consistency with our existing UX (i.e. we don't want to redirect visitors to another page)
Any pointers gratefully received.