Earlier quoted context omitted.
flex everything, it behaves much smoother
I've struggled with children sizing in flex. Children take up more space depending on their content. If the content overflows, flex doesn't handle that well either. Grid seems to handle this better when you specify grid-template-column. Anybody know a good flex-specific solution?
The searchable keyword for that is "responsive".
Using length units related to viewport size on max-widht may help.