Core value: The ability for someone to add Bootstrap 4 to their resumé in 24 hours or less.
Problem: Existing books/courses re-explain what is already found in the official docs, is often out of date, takes too much time, hard to distribute to a classroom or team, not written for beginners, and it's hard to get help if you have questions.
This reference will help you write flexbox CSS properties as well as find the necessary Bootstrap 4 flex utility classes in order to make a responsive layout.
Bootstrap 4 Quick StartBootstrap 4 training and certification for beginners