Four Card Feature Section using Flexbox

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

Made with the help of a video by Kevin Powell, with my own adjustments. I figured i should mention this for the sake of fairness. I found this website thanks to this video.

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

I found the coloured top of the cards to be challenging, in this example the Top border was coloured, but i don't feel like that is the correct method. I like this version so i have not looked for another solution, my best guess would be to maybe float a coloured element on top of the cards.

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

I suppose my biggest question would be in regards to responsiveness, with how many different screen sizes there are i am unsure how many of them i should be accounting for when writing media queries for example.