Four card section - Need help for responsivity

Hello guys,

Hope you're doing great ! Just finished this project. I must say I am really proud of myself. When I started this one I had absolutely no idea how to display those fours containers but thanks to Google I managed :D

I only have one issue though: I used media query to make my project responsive. It works BUT only on desktop, it doesn't work when I open the website on my phone. I had the same issue for all my projects (realising just now) and I have no idea why. The media query looks fine.

Could you please have a quick look at my CSS file, right at bottom, to see what's wrong ?

Cheers !