I'm not familiar with applets, as I previously stated. So hopefully someone with better experience will assist you. I will just add that the buttons appear - only when you hover over their area with your mouse.... so maybe it's a focusing issue? Or something to do with having them show by default? Have you looked over the
official docs? I also notice you don't call start() even though it's automatically called after init() you don't seem to have an implementation for it...
EDIT: also, you should apply this to your html page if that's where you are planning to deploy it. I just now put it on a simple html page and it functioned as it should have, with the buttons appearing upon page opening.