Stuck in css positioning

I have been in web dev around 3 years. I used for web design libraries and i found it very handy and helpful. But now, i am trying to build with pure css. I found it hard especially with positioning.
I get back to FCC web design certificate and i complete it but it wasn’t that helpful.
Is there anyone who had this problem or only me ?
Who can recommend a great css course?
How can i get over this problem, it really makes me uncomfortable with all that stuff try to do?