Javascript used, only used flexbox , bootstrap cards

I couldn't add responsiveness by myself, I had to use bootstrap to do it for me. I can't still figure out how can I send someone to the border country after clicking it, It's because I did not use any backend. It's just plain js html css api. I'm learnt about URLSearchParams and new methods like .join split .map etc. The most thing that was difficult was the search filter. I was using an array taken from the .card class. Thats why when i searched for a country it at first appeared by later i had to refresh the page to make it work properly, as the array was constantly being changed, But now i've fixed that by just changing the display. and one question. sometimes margin auto just dosen't work I dont know why? What is the proper and best way to add responsiveness? I don't understand how this position property works!