HTML: HyperText Markup Language | MDN
Summary
The HTML section of MDN Web Docs contains information on various aspects of HTML. There are pages for HTML elements (such as <head>, <body>, <header>, <nav>, <main>, and <footer>, amongst others) and for HTML attributes (such as class, id, href, src, style, and lang, amongst others).
CSS: Cascading Style Sheets | MDN
Summary
The CSS section of MDN Web Docs contains information on various aspects of CSS. There are pages for CSS selectors (such as *, >, +, ˜, #, and ., amongst others) and for CSS properties (such as color, background-color, margin, padding, display, and float, amongst others).
Document Object Model (DOM) — Web APIs | MDN
Summary
The DOM section of MDN Web Docs contains information on various apsects of the DOM. There are pages that contain guides relating to the DOM, and there are a small number of pages for DOM interfaces (such as Attr, Document, Element, Event, Node, and XMLDocument, amongst others).
JavaScript | MDN
Summary
The JavaScript section of MDN Web Docs contains information on various aspects of JavaScript. The many pages in this section cover numerous JavaScript topics, from the most basic to the most complex.
Grand Summary
It is important to use only trusted resources so that the information you gather is accurate and up-to-date. Using trusted souces also significantly lessens the risk of infecting your device with malware and/or viruses.