rgb ( 255, 0, 0 )), RGBA values that specify both color and alpha transparency (e.g. # FF0000, also abbreviated as # F00), RGB values on a 0 to 255 scale (e.g. Values may be keywords, such as "center" or "inherit", or numerical values, such as 200px (200 pixels), 50vw (50 percent of the viewport width) or 80% (80 percent of the parent element's width).Ĭolor values can be specified with keywords (e.g. Some properties can affect any type of element, and others apply only to particular groups of elements. Each property has a set of possible values. Properties are specified in the CSS standard. Optional white-space may be around the declaration block, declarations, colons, and semi-colons for readability. Declaration Įach declaration itself consists of a property, a colon ( :), and a value. m圜lass ) enclosing a semicolon-separated list of declarations. Multiple simple selectors may be joined using combinators to specify elements by location, element type, id, class, or any combination thereof. Note the distinction between the double-colon notation used for pseudo-elements and the single-colon notation used for pseudo-classes. It is appended to a selector as in a : hover or # elementid : hover.Ī pseudo-class classifies document elements, such as : link or : visited, whereas a pseudo-element makes a selection that may consist of partial elements, such as :: first-line or :: first-letter. One example of a widely used pseudo-class is : hover, which identifies content only when the user "points to" the visible element, usually by holding the mouse cursor over it. Pseudo-classes are used in CSS selectors to permit formatting based on information that is not contained in the document tree. An ID may only be applied to a single element. A class may apply to any number of instances of any element. elements depending on how they are placed relative to others in the document tree.Ĭlasses and IDs are case-sensitive, start with letters, and can include alphanumeric characters, hyphens, and underscores.class: an identifier that can annotate multiple elements in a document, denoted by a dot prefix e.g.classname (the phrase "CSS class", although sometimes used, is a misnomer, as element classes-specified with the HTML class attribute-is a markup feature that is distinct from browsers' CSS subsystem and the related W3C/WHATWG standards work on document styles see RDF and microformats for the origins of the "class" system of the Web content model).id: an identifier unique within the document, denoted in the selector language by a hash prefix e.g.elements specified by attribute, in particular:.In CSS, selectors declare which part of the markup a style applies to by matching tags and attributes in the markup itself. For non-CSS use of element classes in HTML, see class attribute (HTML). CSS is also used in the GTK widget toolkit.ĬSS has a simple syntax and uses a number of English keywords to specify the names of various style properties. In addition to HTML, other markup languages support the use of CSS including XHTML, plain XML, SVG, and XUL. The W3C operates a free CSS validation service for CSS documents. Internet media type ( MIME type) text/css is registered for use with CSS by RFC 2318 (March 1998). The CSS specifications are maintained by the World Wide Web Consortium (W3C). This cascading priority scheme is predictable. The name cascading comes from the specified priority scheme to determine which style rule applies if more than one rule matches a particular element. CSS also has rules for alternate formatting if the content is accessed on a mobile device. Separation of formatting and content also makes it feasible to present the same markup page in different styles for different rendering methods, such as on-screen, in print, by voice (via speech-based browser or screen reader), and on Braille-based tactile devices. css file to be cached to improve the page load speed between the pages that share the file and its formatting. css file, which reduces complexity and repetition in the structural content and enable the. This separation can improve content accessibility provide more flexibility and control in the specification of presentation characteristics enable multiple web pages to share formatting by specifying the relevant CSS in a separate. ĬSS is designed to enable the separation of content and presentation, including layout, colors, and fonts. CSS is a cornerstone technology of the World Wide Web, alongside HTML and JavaScript. Cascading Style Sheets ( CSS) is a style sheet language used for describing the presentation of a document written in a markup language such as HTML or XML (including XML dialects such as SVG, MathML or XHTML).
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