Clipboard landing page challenge using flex and grid

Hello, I started this challenge very well and was thinking that would be done quickly but as usual i made wrong choice and had to redo it. Then I faced few problem to layout everything. For the first time i use the mobile first design (not easy even if im sure it is the best way). Then I had problem with the layout of the first picture. Finally i manage to put everything in place. I will be very grateful for your feedback especially concerning my CSS code. Is is stodgy but i spent so much time to finish my challenge that i'm afraid to break everything by re-arranging it;-) Enjoy coding !