With the title 'Web Fundamentals', from Google there might be something good there to learn. Butm three points: (1) "Multi-screen" is not in my Funk and Wagnalls and, thus, has a specialized meaning, is a 'term', and needs at least a definition and likely also motivation, explanation, and examples. So, the author of this course on writing Web sites doesn't know how to write. (2) He says that the course will end with…
Multi-screen/Multi-device was the term we chose because mobile-first is a very very loaded and our goal is to target mobile as a base but ensure everyone builds up from that experience. But you are correct, it needs to be introduced.
[Edit] - adding bugs https://github.com/google/WebFundamentals/issues/17 https://github.com/google/WebFundamentals/issues/18