Annnddd this is exactly why I think freeCodeCamp needs to restructure their "curriculum."
You should be able to answer this question yourself. Here. let's keep it simple:
This is part of the Linux Kernel. It is written in C. Go read some code real quick then come back to this post.
Now, you tell me. Is it a good idea to "learn the Linux Kernel" without learning or before you learn C, when in fact the kernel is written in C? No, that makes absolutely no sense and it's going to damage your learning experience in the long run.
The same applies to Bootstrap and CSS. Bootstrap is a CSS/HTML framework. This means that it is written in CSS. Why on earth would you think you don't need to learn CSS "after" Bootstrap? You should learn it BEFORE Bootstrap.
More importantly than any of that though, is you need to improve your ability to figure this kind of stuff out on your own. This entire question is ridiculous and I'm not saying that to be mean, but I'm saying that because I don't see you having a very fun or rewarding coding career if you can't figure this type of stuff out because the problems get MUCH MUCH harder than this. For example, if you go to en.wikipedia.org/wiki/Bootstrap_(front-end_framew…) you will immediately see that Bootstrap is a HTML/CSS template so you can reason to yourself like this: "Well, if I want to be good at HTML/CSS and have a full understanding of front-end web development, because I want to be a good front-end developer, then I'd like to MASTER HTML,CSS,JavaScript so that I can build amazing, custom-built websites for clients or for my own enjoyment."
You don't think like this: "Ugh... I am developer. Do I really need to learn how this crap really works? What's the least amount of learning/work I can get away with? Should I Bootstrap after CSS?"
That's very bad and it makes you a terrible developer. We can't teach you that, you have to determine that for yourself. The other thing too, your post looks like you put no effort into it. I know this is true rather than you just being new to the language because you correctly spelled some words and then misspelled those same words after. That means you didn't put in effort. Your post makes little sense and is riddled with English syntax errors. Good luck if you plan on coding like that. You will have many treacherous and frustrating times ahead.