Learn Responsive Design

web.dev course by Jeremy Keith

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 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. Also, as Jeremy is pointing out:

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

That makes responsive design an accessibility topic as well.