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

https://watch.screencastify.com/v/3eEfSmMej0Ql3SN5rUSD

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.