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:

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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);) .

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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.

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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.

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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.

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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.

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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

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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.

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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.

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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.

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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

Advanced CSSOM View Guide Screen Orientation

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