once you have the event, you can read out the
current screensize (already works), and update the positions of
your panels (and whatever else needs to be adapted)

Some small recent games of mine:
Griefer 4k http://damocles11.byethost9.com/griefer4k.html
Kobold 4k http://damocles11.byethost9.com/kobold.html
Cave 4k http://damocles11.byethost9.com/cave4k.html