Bootstrap is highly opinionated imho, i.e. it's great if you want to do something that lies within its style or else you'll have a hard time. If that's your case, and of course if this is a possibility, you can consider moving to another framework - say, Tailwind.
CSS
I like that it has built in mobile friendliness and a way to just make text fit buy filling in and auto adding the padding needed. What is tailwind?
If you add Bootstrap to your site, you write bootstrap-configuration for it, not normal CSS. You can't use any of the usual code people pass around.
Also, it seems you are doing it for learning, so it wouldn't apply, but a lot of the tricks for eliminating aren't really practical and are best not deployed on real things.
That said, insulating Bootstrap into a layer deeper than your code may help (look at CSS layers). And yeah, like the sibling said, writing it on the browser dev tools is much better than reloading.
I am doing it for learning as well as it being my personal site. It's an "indie-web" kind of project not for any sort of business thing but just to be my corner of the web.
I'll try to do it in the dev browser tools
I reinforce the suggestion of insulating Bootstrap on a layer.
And also, don't be afraid to delete code that is demanding too much maintenance. Don't get attached to it.
Outside of that, have fun!