System variable(s) used to unlock the menu links?

Thanks! This is super helpful and very clever. The only potential problem I saw: if you click the Restrict button a couple of times in a row (instead of alternating between Restrict and Free), it keeps adding duplicate overlay boxes. The Free button will only remove one of those. I figure you could either have the Restrict button disable itself, or what I've done is added a few lines to check if there's already an overlay and nested the createElement code inside of an if statement.

let boxTest = document.getElementById('olID');
let b = boxTest ? true : false;

if (!b) { ...then your code...}