For all other shapes and buttons that we're using throughout the site, I've been able to style them and add desired hover actions.
For the Submit buttons on questions added in Create, however, I am unable to style a button as needed. The fill, border, text color, and hover action should be customizable.
I agree with this and would add that it would be good if you could also customize the text. There is the option to customize the text but it doesn't carry through to the end user.