Four Card Feature Section

I used flexbox and did out two more breakpoints just to practice. I used rem in font-sizes and pixels in the others properties. I tried with rem in everything but it was a chaos to do the breakpoints correctly so I changed back to pixels. I changed the lightness of Grayish Blue color from 66% to 45% due to contrast ratio issues. By the way, very common in Frontend Mentor Challenges. The card top border radius only affects the border in the design - and not the element itself, but I did not find a way to change that with css. Any suggestion will be appreciated.