The first row of buttons does not consist of 'real' buttons, they are containers, styled to look like buttons. Without the styling they would appear just as underlined words. But much can be done with styling, both with colours, image background and hover effects. These are the buttons that can be used e.g. as CTA (call to action) or menu items in navigations.
In the middle are the 'real buttons'- unstyled - as found among the Editor's form items. They probably don't look very interesting until they get some styling, so at the bottom some different shapes have been applied.
All the styling, both shapes, colours and other effects can be used for all the buttons.
Download the component.