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The basic goal of the Cascading Stylesheet (CSS) language is to allow a browser engine to paint elements of the page with specific features, like colors, positioning, or decorations. The CSS syntax reflects this goal and its basic building blocks are:
Beginner beginner CSS Guide Web

Using CSS variables

CSS Variables are entities defined by CSS authors which contain specific values to be reused throughout a document. They are set using custom property notation (e.g. --main-color: black;) and are accessed using the var() function (e.g. color: var(--main-color);) .
CSS CSS Variables Guide Web

Using the Performance API

A fundamental requirement of web performance is a precise and consistent definition of time. The DOMHighResTimeStamp type (a double) is used by all performance interfaces to hold such time values. Additionally, there must be a way to create a timestamp for a specific point in time; this is done with the now() method.
Guide performance Performance Web Performance

Improving compatibility using WebRTC adapter.js

While the WebRTC specification is relatively stable, not all browsers have fully implemented all of its features. In addition, some browsers still have prefixes on some or all WebRTC APIs. While you can manually code around these issues, there is an easier way. The WebRTC organization provides on GitHub the WebRTC adapter to work around compatibility issues in different browsers' WebRTC implementations. The adapter is a JavaScript shim which lets your code to be written to the specification so that it will "just work" in all browsers with WebRTC support. There's no need to conditionally use prefixed APIs or implement other workarounds.
API Audio Guide Video WebRTC

JavaScript Guide

The JavaScript Guide shows you how to use JavaScript and gives an overview of the language. If you need exhaustive information about a language feature, have a look at the JavaScript reference.
Guide JavaScript l10n:priority


Functions are one of the fundamental building blocks in JavaScript. A function is a JavaScript procedure—a set of statements that performs a task or calculates a value. To use a function, you must define it somewhere in the scope from which you wish to call it.
Beginner beginner Functions Guide JavaScript

Keyed collections

This chapter introduces collections of data which are ordered by a key; Map and Set objects contain elements which are iterable in the order of insertion.
Collections Guide JavaScript Map set

Using CSS multiple backgrounds

With CSS3, you can apply multiple backgrounds to elements. These are layered atop one another with the first background you provide on top and the last background listed in the back. Only the last background can include a background color.
CSS CSS Background Example Guide Intermediate NeedsCompatTable

Using CSS multi-column layouts

The CSS multi-column layout extends the block layout mode to allow the easy definition of multiple columns of text. People have trouble reading text if lines are too long; if it takes too long for the eyes to move from the end of the one line to the beginning of the next, they lose track of which line they were on. Therefore, to make maximum use of a large screen, authors should have limited-width columns of text placed side by side, just as newspapers do.
Advanced CSS Guide Multi-columns Web


Specificity is the means by which browsers decide which CSS property values are the most relevant to an element and, therefore, will be applied. Specificity is based on the matching rules which are composed of CSS selectors of different sorts.
Beginner beginner CSS Example Guide Web

Drawing DOM objects into a canvas

Although it's not trivial (for security reasons), it's possible to draw DOM content—such as HTML—into a canvas. This article, derived from this blog post by Robert O'Callahan, covers how you can do it securely, safely, and in accordance with the specification.
Canvas DOM Guide HTML Intermediate SVG


Before we look at the transformation methods, let's look at two other methods which are indispensable once you start generating ever more complex drawings.
Canvas Graphics Guide HTML HTML5 Intermediate Web