button and Group (which button is extended from) don't have a focusPercent field, afaik.
You could do this; In your .brs script, add an observer to the button's focusedChild:
' the button has focus, decorate accordingly'
' the button lost focus, undecorate accordingly'
Actually you probably need to use "m.top" instead of "m.button" assuming this script is in the actual button brs.