How to make adaptive?

Question

css

I am doing a project here is a small piece of it

https://codepen.io/Dunhil/pen/gOxVYZB

For phone and tablet everything works as it should. Feel free to check. And on the desktop it hung ((
It is necessary that it beat on the mobile phone as it is now. And for the desktop, so that the two sections are combined into one and beat on the floors of the screen.

When I eat, make a common section and for the screen more than 974px, make sections flex plus minus something is done as it should NOOO layout on mobile and tablet breaks.Tell me
how to do this so as not to break the whole mile away.