I would recommend using the new Button Set component in Brooklyn release. There is a standard property to adjust the alignment of the buttons (left, center, right). That way, you won't have to bother with any CSS.
If you absolutely must keep the old buttons on a page title, what I used to do is place the page title component inside a responsive grid which had 3 divisions...placing the page title in the center division and setting the division width property to "Fit to Content". Then I removed the title and sub-title from the page Title. That way, it would float nicely in the center of the responsive grid.
But again, the new button set component was designed specifically for that purpose.