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 (including XML dialects such as SVG, MathML or XHTML). CSS is a cornerstone technology of the 

CSS is designed to enable the separation of presentation and content, including 

; provide more flexibility and control in the specification of presentation characteristics; enable multiple 

 to share formatting by specifying the relevant CSS in a separate .css file, which reduces complexity and repetition in the structural content; and enable the .css file to be 

 to improve the page load speed between the pages that share the file and its formatting.

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 

 tactile devices. CSS also has rules for alternate formatting if the content is accessed on a 

 comes from the specified priority scheme to determine which style rule applies if more than one rule matches a particular element. This cascading priority scheme is predictable.

The CSS specifications are maintained by the 

) text/css is registered for use with CSS by RFC 2318 (March 1998). The W3C operates a free 

In addition to HTML, other markup languages support the use of CSS including 

 and uses a number of English keywords to specify the names of various style properties.

. Each rule or rule-set consists of one or more 

 declare which part of the markup a style applies to by matching tags and attributes in the markup itself.

 of a specific type, e.g. the second-level headers 

: an identifier unique within the document, identified with a hash prefix e.g. #id

: an identifier that can annotate multiple elements in a document, identified with a period prefix e.g. .classname

elements depending on how they are placed relative to others in the 

Classes and IDs are case-sensitive, start with letters, and can include alphanumeric characters, hyphens, and underscores. A class may apply to any number of instances of any elements. An ID may only be applied to a single element.

 are used in CSS selectors to permit formatting based on information that is not contained in the document tree. 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. It is appended to a selector as in a:hover or #elementid:hover. A pseudo-class classifies document elements, such as :link or :visited, whereas a 

 makes a selection that may consist of partial elements, such as ::first-line or ::first-letter.Note the double-colon notation for pseudo-elements versus single-colon notation for pseudo-class.

Selectors may be combined in many ways to achieve great specificity and flexibility. Multiple selectors may be joined in a spaced list to specify elements by location, element type, id, class, or any combination thereof. The order of the selectors is important. For example, div .myClass {color: red;} applies to all elements of class myClass that are inside div elements, whereas .myClass div {color: red;} applies to all div elements that are inside elements of class myClass. This is not to be confused with concatenated identifiers such as div.myClass {color: red;} which applies to div elements of class myClass.

The following table provides a summary of selector syntax indicating usage and the version of CSS that introduced it.

 on 10 October 1994.At the time, Lie was working with 

. Several other style sheet languages for the web were proposed around the same time, and discussions on public mailing lists and inside 

 resulted in the first W3C CSS Recommendation (CSS1) being released in 1996. In particular, a proposal by 

 was influential; he became co-author of CSS1, and is regarded as co-creator of CSS.

Style sheets have existed in one form or another since the beginnings of Standard Generalized Markup Language (

) in the 1980s, and CSS was developed to provide style sheets for the web.One requirement for a web style sheet language was for style sheets to come from different sources on the web. Therefore, existing style sheet languages like 

 were not suitable. CSS, on the other hand, let a document's style be influenced by multiple style sheets by way of "cascading" styles.

As HTML grew, it came to encompass a wider variety of stylistic capabilities to meet the demands of 

. This evolution gave the designer more control over site appearance, at the cost of more complex HTML. Variations in 

,made consistent site appearance difficult, and users had less control over how web content was displayed. The browser/editor developed by Tim Berners-Lee had style sheets that were hard-coded into the program. The style sheets could therefore not be linked to documents on the web.

, also of CERN, wanted to separate the structure from the presentation so that different style sheets could describe different presentation for printing, screen-based presentations, and editors.

Improving web presentation capabilities was a topic of interest to many in the web community and nine different style sheet languages were proposed on the www-style mailing list. Of these nine proposals, two were especially influential on what became CSS: Cascading HTML Style Sheets and Stream-based Style Sheet Proposal (SSP). Two browsers served as testbeds for the initial proposals; Lie worked with 

 browser. Bert Bos implemented his own SSP proposal in the 

 browser. Thereafter, Lie and Bos worked together to develop the CSS standard (the 'H' was removed from the name because these style sheets could also be applied to other markup languages besides HTML).

" conference (later called WWW2) in Chicago, Illinois in 1994, and again with Bert Bos in 1995. Around this time the W3C was already being established, and took an interest in the development of CSS. It organized a workshop toward that end chaired by 

. This resulted in W3C adding work on CSS to the deliverables of the HTML editorial review board (ERB). Lie and Bos were the primary technical staff on this aspect of the project, with additional members, including 

 of Microsoft, participating as well. In August 1996, 

 presented an alternative style sheet language called 

 (JSSS). The spec was never finished, and is deprecated. By the end of 1996, CSS was ready to become official, and the CSS level 1 Recommendation was published in December.

 had all been taking place in one group, the HTML Editorial Review Board (ERB). Early in 1997, the ERB was split into three working groups: 

 of W3C; DOM Working group, chaired by Lauren Wood of 

The CSS Working Group began tackling issues that had not been addressed with CSS level 1, resulting in the creation of CSS level 2 on November 4, 1997. It was published as a W3C Recommendation on May 12, 1998. CSS level 3, which was started in 1998, is still under development as of 2014.

In 2005, the CSS Working Groups decided to enforce the requirements for standards more strictly. This meant that already published standards like CSS 2.1, CSS 3 Selectors, and CSS 3 Text were pulled back from Candidate Recommendation to Working Draft level.

CSS CheatSheet

 for documents designed to be displayed in a 

. It can be assisted by technologies such as 

 the documents into multimedia web pages. HTML describes the structure of a 

 and originally included cues for the appearance of the document.

 are the building blocks of HTML pages. With HTML constructs, 

 may be embedded into the rendered page. HTML provides a means to create 

 for text such as headings, paragraphs, lists, 

, quotes and other items. HTML elements are delineated by 

. Tags such as <img /> and <input /> directly introduce content into the page. Other tags such as <p> surround and provide information about document text and may include other tags as sub-elements. Browsers do not display the HTML tags but use them to interpret the content of the page.

, which affects the behavior and content of web pages. Inclusion of CSS defines the look and layout of content. The 

 (W3C), former maintainer of the HTML and current maintainer of the CSS standards, has encouraged the use of CSS over explicit presentational HTML since 1997.

, is used to display video and audio, primarily using the <canvas> element, in collaboration with javascript.

, a system for CERN researchers to use and share documents. In 1989, Berners-Lee wrote a memo proposing an 

 system. Berners-Lee specified HTML and wrote the browser and server software in late 1990. That year, Berners-Lee and CERN 

 collaborated on a joint request for funding, but the project was not formally adopted by CERN. In his personal notes from 1990 he listed "some of the many areas in which hypertext is used" and put an 

The first publicly available description of HTML was a document called 

, first mentioned on the Internet by Tim Berners-Lee in late 1991.

 It describes 18 elements comprising the initial, relatively simple design of HTML. Except for the hyperlink tag, these were strongly influenced by 

 (SGML)-based documentation format at CERN. Eleven of these elements still exist in HTML 4.

 text, images, and other material into visual or audible web pages. Default characteristics for every item of HTML markup are defined in the browser, and these characteristics can be altered or enhanced by the web page designer's additional use of 

. Many of the text elements are found in the 1988 ISO technical report TR 9537 

, which in turn covers the features of early text formatting languages such as that used by the 

 (Compatible Time-Sharing System) operating system: these formatting commands were derived from the commands used by typesetters to manually format documents. However, the SGML concept of generalized markup is based on elements (nested annotated ranges with attributes) rather than merely print effects, with also the separation of structure and markup; HTML has been progressively moved in this direction with CSS.

Berners-Lee considered HTML to be an application of SGML. It was formally defined as such by the 

 (IETF) with the mid-1993 publication of the first proposal for an HTML specification, the "Hypertext Markup Language (HTML)" Internet Draft by Berners-Lee and 

 to define the grammar. The draft expired after six months, but was notable for its acknowledgment of the 

 browser's custom tag for embedding in-line images, reflecting the IETF's philosophy of basing standards on successful prototypes. Similarly, 

's competing Internet-Draft, "HTML+ (Hypertext Markup Format)", from late 1993, suggested standardizing already-implemented features like tables and fill-out forms.

After the HTML and HTML+ drafts expired in early 1994, the IETF created an HTML Working Group, which in 1995 completed "HTML 2.0", the first HTML specification intended to be treated as a standard against which future implementations should be based.

Further development under the auspices of the IETF was stalled by competing interests. Since 1996, the HTML specifications have been maintained, with input from commercial software vendors, by the 

 (W3C).However, in 2000, HTML also became an international standard (

 15445:2000). HTML 4.01 was published in late 1999, with further errata published through 2001. In 2004, development began on HTML5 in the 

Web Hypertext Application Technology Working Group

 (WHATWG), which became a joint deliverable with the W3C in 2008, and completed and standardized on 28 October 2014.

November 24, 1995HTML 2.0 was published as 

January 14, 1997HTML 3.2 was published as a 

. It was the first version developed and standardized exclusively by the W3C, as the IETF had closed its HTML Working Group on September 12, 1996.Initially code-named "Wilbur", HTML 3.2 dropped math formulas entirely, reconciled overlap among various proprietary extensions and adopted most of 

 were omitted due to a mutual agreement between the two companies. A markup for mathematical formulas similar to that in HTML was not standardized until 14 months later in 

December 18, 1997HTML 4.0 was published as a W3C Recommendation. It offers three variations:

Strict, in which deprecated elements are forbidden

Transitional, in which deprecated elements are allowed

Initially code-named "Cougar", HTML 4.0 adopted many browser-specific element types and attributes, but at the same time sought to phase out Netscape's visual markup features by marking them as 

 in favor of style sheets. HTML 4 is an SGML application conforming to ISO 8879 – SGML.April 24, 1998HTML 4.0 was reissued with minor edits without incrementing the version number.December 24, 1999HTML 4.01 was published as a W3C Recommendation. It offers the same three variations as HTML 4.0 and its last 

 were published on May 12, 2001.May 2000ISO/IEC 15445:2000 ("

 HTML", based on HTML 4.01 Strict) was published as an ISO/IEC international standard. In the ISO this standard falls in the domain of the 

 (ISO/IEC Joint Technical Committee 1, Subcommittee 34 – Document description and processing languages).After HTML 4.01, there was no new version of HTML for many years as development of the parallel, XML-based language XHTML occupied the W3C's HTML Working Group through the early and mid-2000s.

October 28, 2014HTML5 was published as a W3C Recommendation.November 1, 2016HTML 5.1 was published as a W3C Recommendation.December 14, 2017HTML 5.2 was published as a W3C Recommendation.

, an informal CERN document listing 18 HTML tags, was first mentioned in public.June 1992First informal draft of the HTML DTD,with seven subsequent revisions (July 15, August 6, August 18, November 17, November 19, November 20, November 22)November 1992HTML DTD 1.1 (the first with a version number, based on RCS revisions, which start with 1.1 rather than 1.0), an informal draft June 1993Hypertext Markup Language was published by the 

 IIIR Working Group as an Internet Draft (a rough proposal for a standard). It was replaced by a second version one month later.November 1993

 was published by the IETF as an Internet Draft and was a competing proposal to the Hypertext Markup Language draft. It expired in July 1994.November 1994First draft (revision 00) of HTML 2.0 published by IETF itself (called as "HTML 2.0" from revision 02), that finally led to publication of 

 in November 1995.April 1995 (authored March 1995)HTML 3.0 was proposed as a standard to the IETF, but the proposal expired five months later (28 September 1995) without further action. It included many of the capabilities that were in Raggett's HTML+ proposal, such as support for tables, text flow around figures and the display of complex mathematical formulas.W3C began development of its own 

 for HTML 3 and Cascading Style Sheets, but HTML 3.0 did not succeed for several reasons. The draft was considered very large at 150 pages and the pace of browser development, as well as the number of interested parties, had outstripped the resources of the IETF. Browser vendors, including Microsoft and Netscape at the time, chose to implement different subsets of HTML 3's draft features as well as to introduce their own extensions to it. (see 

). These included extensions to control stylistic aspects of documents, contrary to the "belief [of the academic engineering community] that such things as text color, background texture, font size and font face were definitely outside the scope of a language when their only intent was to specify how a document would be organized." Dave Raggett, who has been a W3C Fellow for many years, has commented for example: "To a certain extent, Microsoft built its business on the Web by extending HTML features."

 by the W3C.Although its syntax closely resembles that of 

 has abandoned any attempt to be an SGML application and has explicitly defined its own "html" serialization, in addition to an alternative XML-based XHTML5 serialization.2011 HTML5 – Last CallOn 14 February 2011, the W3C extended the charter of its HTML Working Group with clear milestones for HTML5. In May 2011, the working group advanced HTML5 to "Last Call", an invitation to communities inside and outside W3C to confirm the technical soundness of the specification. The W3C developed a comprehensive test suite to achieve broad interoperability for the full specification by 2014, which was the target date for recommendation. In January 2011, the WHATWG renamed its "HTML5" living standard to "HTML". The W3C nevertheless continues its project to release HTML5.2012 HTML5 – Candidate RecommendationIn July 2012, WHATWG and 

 decided on a degree of separation. W3C will continue the HTML5 specification work, focusing on a single definitive standard, which is considered as a "snapshot" by WHATWG. The WHATWG organization will continue its work with HTML5 as a "Living Standard". The concept of a living standard is that it is never complete and is always being updated and improved. New features can be added but functionality will not be removed.In December 2012, W3C designated HTML5 as a Candidate Recommendation. The criterion for advancement to 

 is "two 100% complete and fully interoperable implementations".2014 HTML5 – Proposed Recommendation and RecommendationIn September 2014, W3C moved HTML5 to Proposed Recommendation.On 28 October 2014, HTML5 was released as a stable W3C Recommendation, meaning the specification process is complete.

XHTML is a separate language that began as a reformulation of HTML 4.01 using 

 1.0. It is no longer being developed as a separate standard.

XHTML 1.0 was published as a W3C Recommendation on January 26, 2000, and was later revised and republished on August 1, 2002. It offers the same three variations as HTML 4.0 and 4.01, reformulated in XML, with minor restrictions.

XHTML 1.1was published as a W3C Recommendation on May 31, 2001. It is based on XHTML 1.0 Strict, but includes minor changes, can be customized, and is reformulated using modules in the W3C recommendation "Modularization of XHTML", which was published on April 10, 2001.

XHTML 2.0 was a working draft, work on it was abandoned in 2009 in favor of work on 

.XHTML 2.0 was incompatible with XHTML 1.x and, therefore, would be more accurately characterized as an XHTML-inspired new language than an update to XHTML 1.x.

An XHTML syntax, known as "XHTML5.1", is being defined alongside 

On 28 May 2019, the W3C announced that WHATWG would be the sole publisher of the HTML and DOM standards.The W3C and WHATWG had been publishing competing standards since 2012. While the W3C standard was identical to the WHATWG in 2007 the standards have since progressively diverged due to different design decisions.The WHATWG "Living Standard" had been the de facto web standard for some time.

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. It is often described as a "batteries included" language due to its comprehensive 

 began working on Python in the late 1980s as a successor to the 

 and first released it in 1991 as Python 0.9.0. Python 2.0 was released in 2000 and introduced new features such as 

 support. Python 3.0, released in 2008, was a major revision that is not completely 

 with earlier versions. Python 2 was discontinued with version 2.7.18 in 2020.

Python consistently ranks as one of the most popular programming languages.

Python was conceived in the late 1980s by 

 operating system. Its implementation began in December 1989.Van Rossum shouldered sole responsibility for the project, as the lead developer, until 12 July 2018, when he announced his "permanent vacation" from his responsibilities as Python's "

", a title the Python community bestowed upon him to reflect his long-term commitment as the project's chief decision-maker.In January 2019, active Python core developers elected a five-member Steering Council to lead the project.

 was initially set for 2015, then postponed to 2020 out of concern that a large body of existing code could not easily be forward-ported to Python 3. No further security patches or other improvements will be released for it. With Python 2's 

, only Python 3.6.x and later were supported. Later, support for 3.6 was also discontinued. In 2021, Python 3.9.2 and 3.8.8 were expedited as all versions of Python (including 2.7) had security issues leading to possible 

In 2022, Python 3.10.4 and 3.9.12 were expedited and so were older releases including 3.8.13, and 3.7.13 because of many security issues. Python 3.9.13 is the latest 3.9 version, and from now on 3.9 (and older; 3.8 and 3.7) will only get security updates.

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C++ is a general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes".

 - C++ supports at least seven different styles of programming. Developers can choose any of the styles.

 - You can use C++ to develop games, desktop apps, operating systems, and so on.

 - Like C programming, the performance of optimized C++ code is exceptional.

 - C++ allows you to divide complex problems into smaller sets by using objects.

C++ is used to develop games, desktop apps, operating systems, browsers, and so on because of its performance.

After learning C++, it will be much easier to learn other programming languages like Java, Python, etc.

C++ helps you to understand the internal architecture of a computer, how computer stores and retrieves information.

CPP Cheatsheet

C is a general-purpose computer programming language. It was created in the 1970s by Dennis Ritchie, and remains very widely used and influential. By design, C's features cleanly reflect the capabilities of the targeted CPUs.

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