After multiple years, CSS is still the most difficult thing I've ever interacted with?

Listen I specifically set the width of something to like 10vw and it just... it just doesn't do anything, it still takes up the entire width for some reason. CSS just doesn't listen. It doesn't throw an error, it just doesn't do anything. And it doesn't do anything ever. I no longer even expect that changing something in a class will actually yield any result

I have 300 lines of CSS for the simplest shit ever, just because, for some reason, shit doesn't work, so I create another div encapsulating it and somehow then it works or doesn't idk. If I want something to do something I go and paste it in every single style until I see something actually happen like so:

    justify-content: flex-start;
    align-items: flex-start;
    align-content: flex-start;

Now I know the difference, theoretically, and how it's supposed to work, theoretically, and seriously, I've never had an issue with Python development, I've never had an issue with JavaScript, but I can't fucking get CSS, last year I made a project that I was pretty proud off with a backend and everything, with all sorts of bells and whistles, but I ended up not ever finishing it because I just could not get CSS to cooperate!

I mean why is there a scrollbar?? How are you making me scroll when you're not supposed to take up any of that space because the container itself is set to a limited VH/VW ??

I don't have specific examples because I have thousands of line of CSS that I have no idea how to make heads or tails out of. Is there a CSSuicide watch helpline of some sort?