Foldable Categories

I saw this plugin created
https://www.mealldubh.org/index.php/software/fold_page_menus/
And was wondering if anyone knew if it could be adapted to categories, or if you knew of any plug ins which would make the categories collapsable or at least hidden.

My site is https://www.widgx.com and if you look at the side bar you’ll see the categories. I wanted it to be that when someone CLICKED “categories” it showed them.

Any suggestions? (besides widgets because I do not know how to update my theme to suppprt widgets and I’ve already tried.)