You can use the button editor to create or edit a button's style. You can create a new style or use preset styles. You could also save the custom style as a new button for using it future use in other sliders and slides.
There are a lot of options for you to style your button and apply them with the option of seeing changes in real-time preview.
If you remove a button from the list it will affect other sliders that use this specific button as well and their style would be removed.