Looking at it slightly differently to Richard... Bootstrap adds unnecessary overhead and slows down the loading of your website.
I find the best solution is to dump frameworks like Bootstrap as you have to bend to their will and make compromises. They were designed years ago to negate the differences and quirks with the browsers, mainly IE. Now, there are effectively 3 different layout engines, Chromium (Chrome, Edge, Opera, brave, Vivaldi, etc..), FireFox, and Safari, and they're pretty close with compatibility, so frameworks like Bootstrap are no longer needed.
There are many top-notch CSS devs out there putting out YouTube videos, blogs/articles, training, etc like
Kevil Powell[
^],
Stephanie Eckles[
^],
Web Dev Simplified[
^] , and many others. Then you have
Can I use...[
^] to help navigate browser compatibility.
The best learning tools are the
browser developer tools[
^] . You can look at pages with content that you want to learn/copy. You can also modify the CSS and learn live.
It's a bit scary at first to remove the bootstrap training wheels, however, long-term, the benefits out weigh the risks and you will find that you can do far more than the limitation of CSS frameworks like Bootstrap.