Any way to add a class to a button?

Hi guys,

I just installed a new plugin I just purchased called Ninja Kick, which uses jQuery to open a contact form slide out from anywhere on the site. All that must be done is add a CSS class to any element and the form opens up when the link is clicked (see here: http://royalties.patriotenergy.com/)

My problem is that there doesn’t appear to be a way to add a CSS class to buttons or button shortcodes within the theme, and my site is already built out with several buttons.

Is there a way to add a CSS class to a button via the interface or shortcode? If not, is this something that can be added?

Thanks guys!

Dave