The issue is that your template is automatically adding a style of "art-button" to all buttons it finds on the page. Then, it's adding special styling for the 'hover' condition of those buttons, which is making it smaller and change you're seeing.
There's not much we can do about this in our module since its your template that's altering the button, adding that class, and then using it's styles 'outside' of the classes we've already assigned to the button. I'm not sure of the best way to fix this other than contacting your template provider and see if they can tell you how to stop adding that class name to the button.
As for inheriting the styles from your template, that's not something we currently support as there are too many templates out there to ensure compatibility with them all. We've tried in the past to do this, but had to lock down our styling a bit more to prevent these types of conflicts from creeping in.
I hope that helps explain, and good luck,
Alex