3column-card component w basic html&css

Hi all, I'm still puzzled as to how I can better improve on my code for better responsive design. As you can see, the card heights are different at certain browser widths (as I've set .card height = auto;). Is there a better way to go about doing this instead?

I have also yet to figure out how I should curve the corners.

It will be nice if you could comment on my post if you have submitted a better solution of your own! I would love to check & study your solution if you don't mind. :-)

Thank you in advance!!