The hidden cost of frustrating, demotivating web development MOOCs!
Great content ya abdelrahman
I am so happy because at the end of the article I discoverd that you are Egyption.
If you mean Precompilers, then as I said, the learning curve is minimal, and it can be used exactly as normal CSS and get fancier incrementally.
If you mean CSSgrid and Flexbox etc… then there is nothing more fundamental to learn, they ARE native CSS, there is zero upside to learn the old way unless you plan to work with internet explorer, which is an edge case and makes it a subject for advanced studies not introduction to CSS!