Responsive layout using CSS flexbox

I tried this challenge before and found it quite difficult but once I discovered flexbox it was a gamechanger! Really sped up the process for me. This is also the first time I have used media query's in a challenge and I'm not sure if I have done it correctly but I am still happy with the outcome. I am still very new to coding so any feedback would be greatly appreciated on how I did my media querys and if my css needs to improve in parts.

Thanks!!