Honestly, the only real advice is the same advice I have been giving for 15 years: go on w3schools and start going through every tutorial on CSS and just start experimenting.
seconding going on w3schools although my go to these days for reference is MDN's web docs (https://developer.mozilla.org/en-US/docs/Web/CSS)! re: templates they're alright but by design they dont necessarily encourage you to properly get your hands dirty
i used this (https://john-doe.neocities.org/) as a base code, which is nice because it gives you everything you need while being endlessly customizable. frankensteining a bunch of css together is what i usually end up doing
thank you for the replies! i am tinkering with my own CSS code now. w3schools is perfect. maybe i'll throw up some ~experimental~ pages on the site somewhere!
gotta be your own biggest fan