Child div goes out of parent div

Hi, I'm new here and thank you for allowing me to be a part of this forum.

I'm struggling for 2 days to find out why this child div is going out of its parent div. I know it's because of margin, but I used margin many times and I never had this type of problem with CSS. I used box-sizing und overflow already, but it's not helping either.

Here is the code: https://jsfiddle.net/nj9594o9/

Any idea what I can change to keep margin inside the parent div?

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