Unresponsive grid

Hi guys, i hope you doing well and safe.

On my landing page project , in responsive web design cert and after hundreds trials I still have an responsiveness issue. In grid-container, there is 3 squares as 3 products carts. using google browser developer option to simulate mobile screen, when I select iPhone-X , 3rd grid is not responsive white the 1st and 2nd are responsive which makes me really crazy and tired :exploding_head:
here is my codepen url codepen url

Please help. If there is a recommendation of free responsive web design tutorials please recommend it to me, my only weak point is mobile responsiveness. Is there any other work method to avoid spending hours in styling css again and again, its a real pain! Or is there software which make the job by automatically scanning html file and adding needed @media screen.

Thank you vey much.
Best Regards