Does anyone know where this site gets their CSS classes from?

I was exploring different sites to use as references and came across https://www.kaizenlabs.co/. Does anyone know where they get their text size css classes from? I absolutely love their method of responsive font scaling based on breakpoints at 30rem and 64rem (classes like t-[#], for ex), and the other classes also seem super useful, but there are sooo many I'm having trouble believing they were custom-ly inputted. Were they? Is it a preset I can find online somewhere, at least part of it? I don't see them anywhere in the base tailwind library, so I know they don't come from there. I checked so many others too, but no dice so far. Thanks in advance!