It's using some animation sugar from jQuery (source is in this blogpost: https://app.trevor.io/public/blog/demo).

It might be possible to port most stuff over to ES6 and use CSS animations; however, the code is concise and readable.

I'm not arguing against jQuery in the abstract, but you can write concise readable vanilla js/css with animations.

I've used jQuery recently because I had to target older browsers, but if you don't it's almost always cleaner and lighter weight to use modern J's.

Honestly, my first thought was to port the code to ES6/CSS3 because I also share the belief that the code can be as concise if not moreso; however, I still think what the author did was a good solution.

I think the tradeoff is if you want to delegate everything (animations and DOM manipulation) to one language using a single library or split things up into two languages with no libraries. I prefer splitting things between JS and CSS, but I'm impressed with how clever, concise, and expressive using jQuery can be.

Yeah, true. Maybe we'll try and port this to CSS animations at some point.