I recently came to realize that CSS is very important before diving into JS. I have worked with different frameworks like Bootstrap and Vuetify. But recently I decided to take one step back and take a course on CSS only.
I had a project which I struggled for days to create styling and all CSS stuff. I used Bootstrap for it but I had issues here and there that I couldn't fix. After finishing 60% of this course I re-made this project design with help of Flexbox and pure CSS, this time it took me only few hours to achieve what I achieved in days before.
For example, I used to use px most of the time and I didn't know what is em and rem. I also didn't understand well what is position.
So as some advise juniors to start with Vanilla JS before frameworks, I think the same applies to CSS and frameworks. Understand CSS well before getting into Frameworks.