Learn CSS on MDN Beginner.
Learn CSS on Web.dev Beginner.
Learn Responsive Design on Web.dev Advanced.
Learn to write better, resilient CSS Layout - Advanced.
HTML elements reference Beginner/advanced.
CSS reference Beginner/advanced.
A Complete Guide to Grid Beginner.
A Complete Guide to Flexbox Beginner.
Centering in CSS: A Complete Guide Beginner.
All the guides from CSS tricks are intersting - Advanced
A collection of code snippets to help you optimize your web projects. Advanced.
Ten modern layouts in one line of CSS Advanced.
Sass Basics Beginner.
The definitive guide to scss Beginner.
Modern CSS Solutions for Old CSS Problems Advanced.
Defensive CSS Advanced.
To be up to date with the last technics / Advanced
Web Dev Simplified Beginner/advanced.
There is a playlist Introduction to CSS & CSS Tutorials
Kevin Powell Beginner/advanced.
Some playlists are for beginners: