Learn Responsive Design

Learn Responsive Design is

A course exploring all aspects of responsive design. Learn how to make sites that look great and work well for everyone.

It´s a web.dev course prepared by Jeremy Keith and it´s high quality - like so often when I´m referring to Jeremy´s work. I found the chapter about Internationalization particularly interesting. Typography and Responsive Images was also standing out to me.

The goal of responsive design is to make your content available to everyone.
Jeremy Keith

That makes responsive design an accessibility topic as well.