Changeing the aplha of a button when pressed

programming flash
1

Here is the code I am using to change the alpha of a button when pressed:

on(release){
setProperty(this,_alpha, “50”);
incorrectSound = new Sound();
incorrectSound.attachSound(“Buzzer”);
incorrectSound.start()
incorrectSound.setVolume(25)

_root.answer = “That is partially correct.”;
_root.total = _root.total+0
}

However, when I press the button - the whole page, not just the button, changes its alpha. Can anyone tell me why?

Thank you.