4-card-feature-section using CSS Flexbox : challenge#1

This is my very first challenge-submission here. I used CSS flexbox for the solution. I was a bit stumped to get the cards in perfect order both in mobile view and in desktop view and at the end put the middle-two cards inside another flexbox to achieve the target. Maybe this wasn't the best approach to the solution. So, I'd love to hear from you guys about what and where could I change and improve my solution.

Thanks a lot and I'm looking forward to more challenges :)