3 columns preview card component-HTML-CSS-1st challenge

Hello, This is my first challenge at all and I'm not sure that i'm doing everything right, first, in my code and secondly, in the publishing of solution and the use of GitHub. You 'd guess that i'm a newbie ;-) Could you just please tell me if there are big mistakes in my code and maybe some way to improve it ? I guess after publishing my solution, i will have access to one of them or maybe at the ones of the community. Your concept is awesome and with freecodecamp and the Mozilla Developer Network, I hope being able soon to become a good frontend developer. Thanks a lot for your website and all the team. Cyril