Beginner Flexbox Four Cards Component

What are you most proud of, and what would you do differently next time?

I'm proud that my solution seems pretty spot-on. However, I think my code is a little disorganized since I'm still learning flexbox. As I continue to learn flexbox's properties, I believe I'll be able to more elegantly and efficiently code these front end sites.

What challenges did you encounter, and how did you overcome them?

I still don't perfectly understand certain flexbox properties. For example, flex-basis is still a fuzzy concept for me. It's the default size of an element based on what? When does it shrink/grow from that size.

What specific areas of your project would you like help with?

I would like to know if I used flexbox efficiently. Sometimes it feels like I'm abusing flexbox, but I'm struggling to my head around other methods that could better position my elements.