I have been recently doing some training (FreeCodeCamp Curriculums and Udemy’s course: The Complete WordPress Website Business Course by Rob Percival – see Recent Certifications). The Responsive Web Design Certification had a lot of information about CSS Flexbox an CSS Grid.
I have used Flexbox occasionally but have not really used CSS Grid since most of my responsive needs have been met by Bootstrap. But sometimes when you use a library you don’t always look thoroughly under the hood.
Anyway, I’ve been looking at Bootstrap 4.3 and it is awesome and uses lots of CSS Flexbox and CSS Grid (plus lots of other smart stuff).