web.dev
web.dev
Performance and accessibility. Not a from-zero course.
The Modern JavaScript Tutorial
javascript.info
Ilya Kantor’s tutorial. Part 1 is language, part 2 is the browser. Tasks sit after almost every article. The English and Russian editions stay in sync more often than most translated books.
Use it as a course, not a search dump: start at the first page if you are new, or jump to promises when you already write loops.
JavaScript
Also in Web
css-tricks
CSS-Tricks guides
Complete guides to Flexbox and Grid.