Hi Caio,
a workaround would be to create your own improved base theme, and add it as a dependency in all your projects. I know this is same amount of work initially as going in and changing the css in all projects, but more maintainable, especially if you would find other stuff in the base theme later on that you are not happy with.
Just out of curiosity, I tried to recreate this problem and it only happens when I use a link and style it as a button, not when I use a button widget. Is there a reason why you don't just use a button widget with method : navigate ? Does a link have behaviour or properties that a button lacks ?
Dorine