For self-study, I recommend the JavaScript.Info website; it has a lot of short, high-quality resources that are helpful to give you a working understanding of JavaScript, which is a critical foundation for mastering any JavaScript framework such as React, etc. For authoritative information on HTML, CSS and JavaScript, see the Mozilla Developer Network's documentation.
The reading items marked with a star (⭐) are tied to the quizzes for the course and therefore you should give them extra attention.
The following e-books also serve as good supplementary reading resources.