Margin around card in bootstrap

Question

I have set margin:15px for card but it is only taking left margin and not the right margin. Also it is expanding towards right by 15px and going out of the container.

https://code.sololearn.com/WzkhXFThQP0Z/?ref=app

Answer 1

Change row row-cols-1 row-cols-md
To = "row row-col-1 row-col-md"

Answer 2

Thanks Reivin, it worked. But on bootstrap website they have many a times used cols and I have also used cols before but why it is not working here. What is the difference between using cols and col.