What kinds of Default CSS(Such as Bootstrap) are there? And, how do you use them?
that's not default css
those are css libraries
and they are like js frameworks, there's an infinite amount of them
imo you shouldn't have to use any of these css libraries, its pretty simple to create all of these features yourself, and it will also have faster load.
they make custom CSS classes to make it easier to animate, or make your website more elegant.
https://ch1ck3ncss.ch1ck3n.repl.co/ <- here is the css library I'm working on
https://getbootstrap.com/docs/5.0/getting-started/introduction/ <- here is bootstrap
https://watercss.kognise.dev/ <- here is water.css, a simple css library in my opinion
https://tailwindcss.com/ <- tailwind css, a very pouplar one!
Bootstrap, this requires a tags for the bootstrap css, js file as well as Jquery, since bootstrap needs it to run.
There is also w3.css, which is W3Schools css library, they say it's easy to use but I've only ever used bootstrap.
Those at the only two serious ones I've heard of.