Oh man, making a 7-segment display was my favorite question to ask frontend developers. Eventually turning it into a real clock if they were fast enough. Captures lots of basic CSS positioning, JS timers behavior and general ideas like breaking things into components etc
Man where were you at when I was getting asked questions "to see if you've prepared for the interview" with leet code for damned UI frontend positions... I loved answering your type of questions and most companies would not do this for some reason.
I'm guessing when you say "ask frontend developers" you mean "at job interviews". But I like to think you mean something like "at cocktail parties" or other social situations.