I Can't Add Buttons To My Game

When I try to add buttons to the menu from the left bar, no button are shown. I don't what should I do to have the buttons. please help.

 

1. Click, drag and drop the button from the left side of BB into your UI

-- a yellow outlined box should appear​

2. Drag and drop a graphic from your computer into the Image window on the right side of BB

-- for example: a text graphic that says "continue" or a coin graphic​

3. Modify the Transform, Image, Function or Action, Sound, and Properties fields on the right side of BB

Practical example: use navigation buttons to link your main UI to your store UI