If you just want brackets, make the button link be text only, and add the brackets as WHITE text (also insert a separate text box between the brackets for the button description — like Button 1, Play All, etc…).
Change the HIGHLIGHT STYLE to “Mask Overlay” (instead of rectangle).
Then modify the Color Sets so that the Selected state uses a fill color with opacity to show the White brackets when you navigate to the button.
Regards,
George