Hey @Adventure4Life wow I'm surprised your question hasn't been answered sooner. Not sure if you've found a fix to your problem yet.

This is not something I have personally done before but I think flixel-ui is something you should look into https://github.com/HaxeFlixel/flixel-ui

Also, there seems to be somewhat of an example here, but it seems quite buggy :( https://haxeflixel.com/demos/Calculator/