How to stylize the EqualTo Validator message in Flask?

I have the validator

EqualTo('pass_confirm', message='Passwords Must Match!')

which when the passwords don’t match shows an error like this.

How do I stylize the error message to be red? I’ve already tried changing the message to a <span style="color:red">, but it renders plain text and not the HTML.

enter image description here

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Author: Alex F