Problems on Mobile display

I still have a lot of troubles in understanding well the UI rules, I don’t even know if I don’t understand flexbox or something else. In my UI modal everything looks fine till I resize for mobile format, when everything just disappears.
I tried to do a modal with a scroll that would contain colums of dynamic filters

It seems that your elements are there, just that their width is too big. You should try setting some of the parent flexboxes and divs to 100% and also change the direction to vertical on mobile.