Mobile First Design using CSS

Had a lot of fun with this one! I decided to do this challenge to improve my layout skills and although I think I improved a lot, I definitely think there are things I could do better:

1. What's the project structure of a Flutter app supposed to look ideally? I've been trying a few different file structures but not sure if what I'm doing is optional.
2. How do I make the child of a Row element stretch vertically to have the same height as the Row itself? I searched online and tried out the solution here, but it didn't work. I was thinking of setting the heights to be the same manually but decided against it since I'd have to keep adjusting the height for different screen sizes.

Any and all feedback is more than welcome! Would love to hear your thoughts. Cheers🎉