I started to layout through display: flex, is it possible to finish it in accordance with the layout?

Question

css

Hello everyone.
I understand, you say the grid is broken here, the designer did it wrong. But still, you need to layout in accordance with the layout, taking into account adaptability. That is, when the resolution is reduced below 768, you need to beautifully reduce the elements into two columns or into one.
Now there is: s92321ux.bget.ru/navy/contact3.html
I have little experience with flexbox, I'm wondering how to do it correctly through flexbox.
I made it with float: s92321ux.bget.ru/navy/contact.html
I made it with inline-block (the difference is not big) s92321ux.bget.ru/navy/contact2.html
I didn't make it with flexbox: s92321ux.bget.ru/navy/contact3. html

Answer 1

www.w3schools.com/css/css_rwd_grid.asp This should help