Nice and impressive collection of CSS... I can't wait to start stealing interesting settings...
But...
In issue Supressing checkboxes · Issue #2646 · laurent22/joplin · GitHub Laurent explicitly states:
There's unfortunately not guarantee that the HTML will remain stable from one version to the next. In general userstyle.css is "use at your own risk" (or better, don't use it, but that's up to the user).
So if the HTML can (and will, and did) change from one version to the next and userstyle.css is officially discouraged, what's the use of having this in Joplin?