CSS: How to center a div CSS Loader

Question

I’m trying to center a pseudo element in order to make the CSS loader responsive, but have yet been unable to do it. any suggestions? Thanks in advance!

Here's my code
https://code.sololearn.com/WMyv7UcxGvRT/?ref=app

Answer 1

Checkout my code

https://code.sololearn.com/Wy982Ri73YM2/?ref=app