extra.js not working for collapsible accordions?

[sccmcca]

I'm trying to code some collapsible accordions with the same code in steps 1 - 3 of this guide: https://www.w3schools.com/howto/howto_js_accordion.asp

The html (which I have in a .md file) and css (in extra.css) appear to be functional, but the javascript (in extra.js) is not, i.e. the panel does not collapse on-click. I have the proper configurations in mkdocs.yml.

Any ideas what could be the issue? Thanks!