This is really nice, and the collection of practical examples is what makes the content here shine.

Presentationally, the emoji are maybe a little overrepresented, but some of the pairings are amusingly clever. Apparently some here don't appreciate the use of progressive disclosure for the navigation, but for content of this length, it's an appropriate alternative to navigating to a new page.

The one thing I'd suggest is limiting the expand/collapse interaction to one open at a time. There isn't really any advantage to having multiple open at once as there isn't a use case for comparing between open boxes, and keeping everything else collapsed makes exploring the index simpler.