Responsive app with React, Mui + Grid

I am really trying to improve my CSS skills, so that was the emphasis here. What can I do better? Are there best practices for building something with multiple layers like this that you suggest? I was having trouble getting the positioning correct across layouts and I'm sure there's an easier way to do it than how I did!

Besides that, I built with React and pulled data from a JSON to mimick an API, and added some small MUI ellipsis menus to show that part of the interface. Let me know if you see anything in the way I am organizing or building components that you would improve upon :)