Outline around button when clicked

programming flash
1

I have created 4 buttons so far and when pressed they change the color of a box on the screen. I will be putting more buttons on the page. When a button is pressed, how can i get a black outline to show around the button to let the person know that was the button they selected–it would then go off when the next button is selected. Im very new to flash so I could realy use your help.

Thanks

red_btn.onRelease = function() {
var boxColor_color = new Color(box_mc);
boxColor_color.setRGB(0xFF0000);
};
orange_btn.onRelease = function() {
var boxColor_color = new Color(littlebox_mc);
boxColor_color.setRGB(0xFF6500);
};
blue_btn.onRelease = function() {
var boxColor_color = new Color(box_mc);
boxColor_color.setRGB(0x0039FF);
};
green_btn.onRelease = function() {
var boxColor_color = new Color(littlebox_mc);
boxColor_color.setRGB(0x0099FF);
};
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