How can we optimise css in a NextJS - Material UI app?

Question

The google core web vitals complain about not having the CSS optimised. Two main points -

1. Reduce unused CSS (recommendation for both mobile and desktop)
2. Minify CSS (recommendation for mobile devices)

I tried optimising the fonts with @font-face but the overall CSS still seems unoptimised. I have a NextJS app and I use MUI for styling.

No CSS modules or styled components are used.