Cascading Style Sheets ( CSS ) is a style sheet used for describing the presentation of a document written in a markup language . [1] ALTHOUGH MOST Often used to set the visual style of web pages and user interfaces written in HTML and XHTML , the language can be applied to-any XML document Including plain XML , SVG and XUL , and is applicable to rendering in speech , or on other media. Along with HTML and JavaScript, CSS is a cornerstone technology, webpages, user interfaces for web applications , and user interfaces for many mobile applications. [2]

CSS is designed primarily for the layout and content, including aspects such as the layout , colors , and fonts . [3] This separation can improve the accessibility of the content of the CSS file. .

Separation of formatting and content makes it possible for the same markup 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 touch devices. It can also display the web page Can also specify a different style, such as a CSS file stored on their computer, to override the one the author specified.

Changes to the graphic design of a document (or hundreds of documents) can be applied quickly and easily, by a few lines in the CSS file, rather than by changing the markup in the documents.

The CSS specification describes a priority scheme to determine which style rules apply to a particular element. In this so-called cascade , priorities (or weights ) are calculated and assigned to rules, so that the results are predictable.

The CSS specifications are maintained by the World Wide Web Consortium (W3C). Internet media type ( MIME type ) text/cssis registered for use with CSS by RFC 2318 (March 1998). The W3C operates a free CSS validation service for CSS documents. [4]



CSS has a simple syntax and uses a number of different keywords.

A style sheet consists of a list of rules . Each rule or rule-set consists of one or more selectors , and a declaration block .


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

Selectors may apply to:

  • all elements of a specific type, eg the second-level headers h2
  • elements specified by attribute , in particular:
    • id : an unique identifier within the document
    • class : an identifier that can annotate multiple elements in a document
  • elements depending on how they are placed in the document tree .

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

Pseudo-classes 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 , which identifies the content when the user “points to” the visible element, usually by holding the mouse cursor over it. It is appended to a selector as in or . A pseudo-class classifies document elements, such as or , whereas a pseudo-element makes a selection that may consist of partial elements, such as or . [5]:hovera:hover#elementid:hover:link:visited::first-line::first-letter

Selectors can be combined in many ways to achieve great specificity and flexibility. [6] Multiple selectors may be joined to a specified location by location, element type, id, class, or any combination thereof. The order of the selectors is important. For example, apply to all elements of myclass that are inseparable from the elements of myclass.div .myClass {color: red;}.myClass div {color: red;}

The following table provides a summary of the use of CSS. [7]

pattern matches First defined
in CSS level
E an element of type E 1
E: link an E element is the source anchor of a hyperlink of which the target is not yet visited (: link) or already visited (: visited) 1
E: active an E element during certain user actions 1
E :: first-line the first formatted line of an E element 1
E :: first-letter the first formatted letter of an E element 1
.c all elements with class=”c” 1
#myid the element with id=”myid” 1
E.warning an E element whose class is “warning” 1
E # myid an element with ID equal to “myid” 1
EF an F element descendant of an E element 1
* any element 2
E [foo] an element with a “foo” attribute 2
E [foo = “bar”] an element whose “foo” attribute value is exactly equal to “bar” 2
E [foo ~ = “bar”] an element whose “foo” attribute value is a list of whitespace-separated values, one of which is exactly equal to “bar” 2
E [foo | = “en”] an E element whose “foo” attribute has a hyphen-separated list of values ​​beginning (from the left) with “en” 2
E: first-child an element, first child of its parent 2
E: lang (fr) an element of type E in language “en” 2
E :: before generated content before an E element’s content 2
E :: after generated content after an E element’s content 2
E> F an elementary child element 2
E + F F element immediately preceded by an E element 2
E [foo ^ = “bar”] an E element whose “foo” attribute value exactly begins with the string “bar” 3
E [foo $ = “bar”] an E element whose “foo” attribute value ends exactly with the string “bar” 3
E [foo * = “bar”] an E element whose “foo” attribute value contains the substring “bar” 3
E: root an E element, root of the document 3
E: nth-child (n) an E element, the n-th child of its parent 3
E: nth-last-child (n) an element, the n-th child of its parent, counting from the last one 3
E: nth-of-type (n) an E element, the n-th sibling of its type 3
E: nth-last-of-type (n) an element, the n-th sibling of its type, counting from the last one 3
E: last-child an elemental element, last child of its parent 3
E: first-of-type an element, first sibling of its type 3
E: last-of-type an E element, last sibling of its type 3
E: only-child an E element, only child of its parent 3
E: only-of-type an E element, only sibling of its type 3
E: empty an element that has no children (including text nodes) 3
E: target an E element being the target of the referring URI 3
E: enabled has user interface element E that is enabled 3
E: disabled a user interface element E that is disabled 3
E: checked a user interface element E that is checked (for instance a radio-button or checkbox) 3
E: not (s) an element that does not match simple selector s 3
E ~ F F element preceded by E element 3

Declaration block

A declaration block consists of a list of declarations in braces. Each declaration itself consists of a property , a colon ( :), and a value . If there are multiple declarations in a block, a semi-colon ( ;) must be inserted to separate each declaration. [8]

Properties are specified in the standard CSS. Each property has a set of possible values. Some properties can affect any type of element, and others apply only to particular groups of elements. [9]

Values ​​can 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 window width). Can be specified with keywords (eg “red”), hexadecimal values ​​(eg # FF0000, also abbreviated as # F00), RGB values ​​on a 0 to 255 scale (eg ), RGBA values eg ), HSL gold or HSLA values ​​(eg , ). [10]rgb(255, 0, 0)rgba(255, 0, 0, 0.8)hsl(000, 100%,50%)hsla(000, 100%, 50%, 80%)


Before CSS, nearly all presentational attributes of HTML documents are contained within the HTML markup. All of the colors, background styles, element alignments, borders and sizes, often repeated, within the HTML. CSS lets authors move much of the information to another file, the style sheet, resulting in much simpler HTML.

For example, headings ( h1elements), sub-headings ( h2), sub-sub-headings ( h3), etc. are defined structurally using HTML. In print and on the screen, choice of font , size , color and emphasis for these elements is presentational .

Before CSS, an HTML document that presents a typographical characteristic h2of the text. This makes documents more complex, larger, and more error-prone and difficult to maintain. CSS allows the separation of presentation from structure. CSS can define color, font, text alignment, size, borders, spacing, layout, and many other typographic features, and can do so independently for on-screen and printed views. CSS also defines non-visual styles, such as reading speed and emphasis for aural text readers. The W3C has now deprecated the use of all presentational HTML markup. [11]

For example, under pre-CSS HTML,

< hd > < font color = "red" > Chapter 1. </ font > </ h1 >

Using CSS, the same element can be used instead of HTML presentational attributes:

< h1 style = "color: red;" > Chapter 1. </ h1 >

The advantages of this, but the power of CSS becomes more apparent when an internal style element is set, or even better, an external CSS file. For example, suppose the document contains the style element:

< style >
h1 { color : red ;}
</ style >

All h1elements in the document will then automatically become explicit. If the author later wanted to make h1elements blue instead,

< style >
h1 { color : blue ;}
</ style >

rather than by laboriously going through the document and changing the color for each individual h1element.

The style of the CSS file is as follows, and is loaded with syntax similar to:

< link href = "path / to / file.css"> rel = "stylesheet" type = "text / css" >

This document is a preview generated by PC users.


CSS information can be provided from various sources. These sources can be the web browser, the user and the author. The information from the author can be further classified into inline, media type, importance, selector specificity, rule order, inheritance and property definition. CSS style information can be in a separate document or it can be embedded into an HTML document. Multiple style sheets can be imported. Different styles can be applied depending on the output device being used; for example, the screen version can be quite different from the printed version, so that authors can tailor the presentation appropriately for each medium.

The style sheet with the highest priority controls the content display. Declarations not set in the highest priority source are passed to a source of low priority, such as the user agent style. This process is called cascading .

One of the goals of CSS is to allow users greater control over presentation. Someone who finds a different style sheet. Depending on the browser and the web site, the user can choose from various styles provided by the designers, or can remove all styles and view the site using the browser’s default styling attributes.

CSS priority scheme (highest to lowest)
Priority CSS source type Description
1 Importance The ‘ ‘ annotation overwrites the previous priority types!important
2 inline A style applied to an HTML element via HTML ‘style’ attribute
3 Media Type A property definition applies to all media types, unless a specific media CSS is defined
4 User defined Most browsers have the accessibility feature: a user defined CSS
5 Selector specificity A specific contextual selector ( ) overwrites generic definition#heading p
6 Rule order Last rule declaration has a higher priority
7 Parent inheritance If a property is not specified, it is inherited from a parent element
8 CSS property definition in HTML document CSS rule or CSS inline style overwrites a default browser value
9 Browser default The lowest priority: browser default value is determined by W3C initial value specifications


Specificity refers to the relative weights of various rules. [12] What determines which styles apply to an element? Based on specification, a simple selector (eg H1) has a specificity of 1, class selectors have a specificity of 1.0, and ID selectors a specificity of 1.0.0. Because the specificity values do not carry over as in the decimal system, commas are used to separate the “digits” [13] (a CSS rule HAVING Elements 11 and 11 classes Would Have a specificity of 11.11, not 121).

Thus the following rules selectors result in the indicated specificity:

Selectors Specificity
H1 {color: white;} 0, 0, 0, 1
P EM {color: green;} 0, 0, 0, 2
.grape {color: red;} 0, 0, 1, 0
P.bright {color: blue;} 0, 0, 1, 1
P.bright EM.dark {color: yellow;} 0, 0, 2, 2
# id218 {color: brown;} 0, 1, 0, 0
1, 0, 0, 0


Consider this HTML fragment:

<! DOCTYPE html>
< html >
 < head >
 < charset meta = "utf-8" > < style > # xyz { color : red ; } </ style > </ head > < body > < p id = "xyz" style = "color: blue;" > To demonstrate specificity </ p > </ body > <

In the above example, the declaration in the styleattribute overrides the one in the <style>element because it has a higher specificity.


Inheritance is a key feature in CSS; it links to the ancestor-descendant relationship to operate. Inheritance is the mechanism by which they are applied not only to a specified element, but also to their descendants. [12] Inheritance related to the document tree, which is the hierarchy of XHTMLelements in a page based on nesting. Descending elements may inherit CSS property values ​​from any ancestor element enclosing them. In general, descendant elements inherit text-related properties, but box-related properties are not inherited. Properties that can be inherited are color, font, letter-spacing, line-height, list-style, text-align, text-indent, text-transform, visibility, white-space and word-spacing. Properties that can not be inherited are background, border, display, float and clear, height, and width, margin, min- and max-height, and -width, outline, overflow, padding, position, text-decoration, vertical-align, and z -index.

Inheritance can be used to avoid declaring certain properties over and over again in a style sheet, allowing for shorter CSS.

Inheritance in CSS is not the same as inheritance in class-based programming languages , where it is possible to define class B as “like class A, but with modifications”. [14] With CSS, it is possible to style an element with “class A, but with modifications”. HOWEVER, it is not feasible to define a CSS class B like that, qui Then Could be used to multiple Style Elements without HAVING to repeat the changes.


Given the following style sheet:

h1 {
 color : pink ;

Suppose there is an h1 element with an emphasizing element (em) inside:

< h1 >
 This is to < em > illustrate </ em > inheritance
 </ h1 >

If no color is assigned to the element, the emphasized word “illustrate” inherits the color of the parent element, h1. The style sheet h1 has the color pink, hence, the element is likewise pink.


Whitespace between properties and selectors is ignored. This code snippet:

body { overflow : hidden ; background : # 000000 ;

is functionally equivalent to this one:

body {
 overflow : hidden ;
 background : # 000000 ;

One common way to CSS format for readability is to indent each property and give it its own line.


CSS 2.1 defines three positioning schemes:

Normal flow
Inline items are laid out in the same way, then starting at a new line below. Block items stack vertically, like paragraphs and like items in a bulleted list. Normal flow also includes relative positioning of block or inline items, and run-in boxes.
A floated item is taken out of the normal flow and shifted to the left or right in the space available. Other content then flows alongside the floated item.
Absolute positioning
An existing item has no place in, and no effect on, the normal flow of other items. It occupies its assigned position in its container independently of other items. [15]

Position property

There are four possible values ​​of the positionproperty. If an item is Positioned in Any Way other than static, Then The further Top properties topbottomleft, and rightare used to Specify offsets and positions.

The default value places the item in the normal flow
The item is placed in the normal flow , and then shifted or offset from that position. Subsequent flow items are laid out as if the item had not been moved.
Specifies absolute positioning . The element is in relation to its nearest non-static ancestor.
The item is absolutely Positioned in a fixed position on the screen Even As the rest of the paper is scrolled [15]

Float and clear

The floatproperty may have one of three values. Absolutely fixed or fixed items can not be floated. Other items are normally circumnavigated, unless they are prevented from doing so by their clearproperty.

The item floats to the left of the line that it would have appeared in; other items may flow around its right side.
The item floats to the right of the line that it would have appeared in; other items may be around its left side.
Forces the element to appear underneath (‘clear’) floated elements to the left ( ), right ( ) or both sides ( ). [15] [16]clear:leftclear:rightclear:both


Håkon Wium Lie , chief technical officer of the Opera Software company and co-creator of the standard CSS web

CSS was first proposed by Håkon Wium Lie on October 10, 1994. [17] At the time, Lie was working with Tim Berners-Lee at CERN . [18] Several other style sheet languages for the web Were Proposed around the time Sami, and discussions on public mailing lists and inside World Wide Web Consortium resulted in the first W3C Recommendation CSS (CSS1) [19] being white released in 1996. In Particular , Bert Bos ‘ proposal Was influential; he became co-author of CSS1 and is regarded as co-creator of CSS. [20]

Style sheets have existed in one form or another of the beginnings of Standard Generalized Markup Language ( SGML ) in the 1980s, and CSS was developed to provide style sheets for the web. [21]One requirement for a web style sheet. Therefore, DSSSL and FOSI were not suitable. CSS, on the other hand, let a document’s style be influenced by multiple style sheets by way of “cascading” styles. [21]

As HTML grew, it came to encompass a broader range of stylistic capabilities to meet the demands of web developers . This evolution gives the designer more control over site appearance, at the cost of more complex HTML. Variations in Web browser implementations, such as ViolaWWW and WorldWideWeb , [22] made easier. The browser / editor developed by Tim Berners-Lee had style sheets that were hard-coded into the program. The style sheets could not be linked to documents on the web. [23] Robert Cailliau, also of CERN, for screen printing, screen-based presentations, and editors. [22]

Improving web presentation capabilities were proposed on the www-style mailing list. [17] Cascading HTML Style Sheets [17] and Stream-based Style Sheet Proposal (SSP). [20] [24] Two browsers served as testbeds for the initial proposals; With Yves Lafon to implement CSS in Dave Raggett ‘s Arena . [25] [26] [27] Bert Bos implemented his own SSP proposal in the Argo browser. [20]Thereafter, Lie and Bos worked together to develop the CSS standard (besides HTML). [18]

This paper was presented at the ” Mosaic and the Web ” conference (later called WWW2) in Chicago, Illinois in 1994, and again with Bert Bos in 1995. [18] Around this time the W3C was already being established, and took an interest in the development of CSS. It’s a workshop towards that end by Steven Pemberton . This resulted in the creation 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 Thomas Reardon of Microsoft , participating as well. In August 1996 Netscape Communication Corporationpresented an alternative style sheet called JavaScript Style Sheets (JSSS). [18] The spec was never finished and is deprecated. [28] By the end of 1996, CSS was ready to become official, and the CSS level 1 Recommendation was published in December.

Development of HTML, CSS, and the DOM , the HTML Editorial Review Board (ERB). Early in 1997, the ERB was split into three working groups : HTML Working Group , chaired by Dan Connolly of W3C; DOM Working group, chaired by Lauren Wood of SoftQuad ; and CSS Working group , chaired by Chris Lilley of W3C.

The CSS Working Group has been 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 text has already been published as CSS 2.1, CSS 3 Selectors and CSS 3.

Difficulty with adoption

The CSS 1 specification was completed in 1996. Microsoft’s Internet Explorer 3 [18] was released in that year, with some limited support for CSS. IE 4 and Netscape 4.x added more support, but it was so incomplete and had many bugs that prevented CSS from being usedfully adopted. It was more than three years before any web browser achieved near-full implementation of the specification. Internet Explorer 5.0 for the Macintosh , shipped in March 2000, was better than 99 percent CSS 1 support, [29] surpassing Opera, which had been the leader since its introduction of CSS support 15 months earlier. Other browsers followed soon afterwards, and many of them added parts of CSS 2.

However, even when later ‘version 5′ browsers began with a fairly full implementation of CSS, they were still incorrect in certain areas and were inconsistent with bugs and other quirks . The inconsistencies and variation in feature media made it difficulty for designers to accomplish achieve a consistent appearance across browsers and platforms , leading to the use of workarounds Such As CSS hacks and filters .

Problems with browsers’ patchy adoption of CSS, along with the original specification, the W3C to revise the CSS 2 standard in CSS 2.1, which moved to support CSS support in HTML browsers. Some CSS 2 properties that have not been successfully implemented have been dropped, and in a few cases, have been changed to include the standard in line with the predominant existing implementations. CSS 2.1 Became a Candidate Recommendation on February 25, 2004, CSS goal 2.1 was pulled back to Working Draft status on June 13, 2005, [30] and only returned to Candidate Recommendation status on July 19, 2007. [31]

In addition to these problems, the .cssextension was used by a software product used to convert PowerPoint files into Compact Slide Show files, [32] so some web servers served all .css[33] as mime type application/x-pointplus[34] rather than text/css.


CSS has various levels and profiles. Each level of CSS builds on the last, typically adding new features and typically denoted as CSS 1, CSS 2, CSS 3, and CSS 4. Profiles are typically a subset of one or more levels of CSS built for a particular device or user interface . Currently there are profiles for mobile devices, printers, and television sets. Profiles should not be confused with media types, which are added in CSS 2.


The first CSS specification to become an official W3C Recommendation is CSS level 1, published on December 17, 1996. Håkon Wium Lie and Bert Bos are credited as the original developers. [35] [36] Among its capabilities are support for

  • Font properties such as typeface and emphasis
  • Color of text, backgrounds, and other elements
  • Text attributes such as spacing between words, letters, and lines of text
  • Alignment of text, pictures, tables and other elements
  • Margin, border, padding, and positioning for most elements
  • Unique identification and generic classification of groups of attributes

The W3C no longer supports the CSS 1 Recommendation. [37]


CSS level 2 specification was developed by the W3C and published as a recommendation in May 1998. A superset of CSS 1, CSS 2 includes a number of new capabilities like absolute, relative, and fixed positioning of elements and z-index , the concept of type, support for aural style sheets [38] and bidirectional text, and new font properties such as shadows.

The W3C no longer supports the CSS 2 recommendation. [39]

CSS 2.1

CSS level 2 revision 1, often referred to as “CSS 2.1”, fixes errors in CSS 2, removes poorly supported or not fully interoperable features. To comply with the W3C Process for standardizing technical specifications, the CSS 2.1 went back and forth between Working Draft status and Candidate Recommendation status for many years. CSS 2.1 first became a Candidate Recommendation on February 25, 2004, but it was reverted to a Working Draft on June 13, 2005 for further review. It was returned to Candidate Recommendation on 19 July 2007 and then updated in 2009.

Went to CSS 2.1 Proposed Recommendation is 12 April 2011. [40] After being white reviewed by the W3C Advisory Committee, It was finally published as a W3C Recommendation is June 7, 2011. [41]

CSS 2.1 was planned as first and last revision of level 2-but low priority work on CSS 2.2 started in 2015.


Taxonomy and status of CSS3 modules . ● Recommendation ● Candidate Recommendation ● Last Call ● Working Draft.

“CSS3” redirects here. For other uses, see CSS3 (disambiguation) .

Unlike CSS 2, which is a large single specification defining various features, CSS 3 is divided into several separate documents called “modules”. Each module adds new capabilities or extended features defined in CSS 2, preserving backward compatibility. Work on CSS level 3 CSS 2 recommendation. The earliest CSS 3 drafts were published in June 1999. [42]

Due to the modularization, different modules have different stability and statuses. [43] As of June 2012, there are over fifty CSS modules published from the CSS Working Group., [42] and four of these have been published as formal recommendations .

  • 2012-06-19: Media Queries
  • 2011-09-29: Namespaces
  • 2011-09-29: Selectors Level 3
  • 2011-06-07: Color

Some modules have Candidate Recommendation ( CR ) status and are considered moderately stable. At CR internship, implementations are advised to drop vendor prefixes. [44]

Summary of main module-specifications [45]
Module Specification title Status Dated
css3-background CSS Backgrounds and Borders Module Level 3 Candidate Rec. Sep 2014
css3-box CSS basic box model Working Draft , Aug 2007
css-cascade-3 CSS Cascading and Inheritance Level 3 Candidate Rec. May 2016
css3-color CSS Color Module Level 3 recommendation Jun 2011
css3-content CSS3 Generated and Replaced Content Module Working Draft Jun 2016
css-fonts-3 CSS Fonts Module Level 3 Candidate Rec. Oct 2013
css3-GCPM CSS Generated Content for Paged Media Module Working Draft May 2014
css3-layout CSS Template Layout Module Note Mar 2015
css3 media queries, Media Queries recommendation Jun 2012
css3-multicol Multi-column Layout Candidate Rec. Apr 2011
css3-page CSS Paged Media Module Level 3 Working Draft Mar 2013
css3-selectors Selectors Level 3 recommendation Sep 2011
css3-ui CSS Basic User Interface Level 3 Module (CSS3 UI) Working Draft Jul 2015


There is no single, integrated CSS4 specification, [46] because it is split into separate “level 4” modules. [47]

Because CSS3 split the CSS language’s definition into modules, the modules have been allowed to level independently. Most modules are level 3 – they build on things from CSS 2.1. A few level-4 modules exist (such as Image Values, [48] [49] Backgrounds & Borders, [50] or Selectors), [51] which builds the functionality of a preceding level-3 module. Other modules referring to all new features, such as Flexbox , have been designated as “level 1”. [52]

The CSS Working Group sometimes publishes “Snapshots”, a collection of all modules and parts that are considered stable, interoperably implemented and hence ready to use. So far, 2007, [53] 2010, [54] 2015. [55] and 2017. [56]

Browser support

Further information: Cascading Style Sheets

Each web browser uses a layout engine to render web pages, and support for CSS functionality is not consistent between them. Because browsers do not parse CSS perfectly, multiple coding techniques have been developed to CSS ( CSS known as CSS hacks or CSS filters). Adoption of new functionality in CSS can be hindered by lack of support in major browsers. For example, Internet Explorer was slow to add support for many CSS 3 features, which slowed adoption of those features and damaged the browser’s reputation among developers. [57]In order to ensure a consistent experience for their users, web developers often test their sites across multiple operating systems, browsers, and browser versions, increasing development time and complexity. Tools such as BrowserStack have been built to reduce the complexity of these environments.

CSS, including CanIUse and the Mozilla Developer Network . In addition, the CSS 3 defines feature queries, which provide a @supportsdirective that will allow developers to target browsers with support for certain functionality directly within their CSS. [58] CSS polyfills Javascript is not supported by older browsers, which are pieces of JavaScript code designed to make behave consistently. These workarounds and the need to support fallback functionality-can add complexity to development projects, and therefore, companies often define a list of browser versions that they will not support.

As websites adopt newer code standards that are incompatible with older browsers, these browsers can be cut off from the Internet (sometimes intentionally). [59] Many of the most popular websites are not only visually degraded on older browsers, but also in the context of CSS, but do not work at all, in large part of the evolution of Javascript and other web technologies.


Some noted limitations of the current capabilities of CSS include:

Selectors are unable to ascend
CSS currently offers no way to select a parent or ancestor of an element that satisfies certain criteria. [60] CSS Selectors Level 4, which is still in Working Draft status, offers such a selector, [61] but only part of the “complete” selector profile, not the “fast” profile used in dynamic CSS styling. [62] A more advanced selector scheme (such as XPath ) would enable more sophisticated style sheets. The Major Reasons for the CSS Working Group Previously Rejecting Proposals for the parent selectors are related to browser performance and incremental rendering issues. [63]
Can not confirm the new scope independently of position
Scoping rules for properties such as z-index look for the closest parent element with a position: absolute or position: relative attribute. This odd coupling has undesired effects. For example, it is impossible to avoid declaring a new situation when one is forced to adjust an element’s position, preventing one from using the desired scope of a parent element.
Pseudo-class dynamic behavior not controllable
CSS implements pseudo-classes that allow a degree of user feedback by conditional application of alternate styles. One CSS pseudo-class, ” “, is dynamic (equivalent of JavaScript “onmouseover”) and has potential for abuse (eg, implementing cursor-proximity popups), [64] CSS has no ability for a client to disable it (no “disable” -like property) or its effects (no “nochange” -like values ​​for each property).:hover
Can not name rules
There is no way to a CSS rule, which would allow (for example) client-side scripts to refer to the rule even if its selector changes.
Can not include styles from a rule into another rule
CSS styles often need to be duplicated in several rules to achieve a desired effect. Some new CSS features have been proposed to solve this, but (as of February, 2016) are not yet implemented anywhere. [65]
Can not target specific text without altering markup
In addition to the pseudo-element, it uses the place-holder elements.:first-letter

Former issues

In addition, several more issues have been presented in prior versions of the standard CSS, but have been alleviated:

Vertical control limitations
Though horizontal placement was often unintuitive, convoluted, or outright impossible. Simple tasks, such as centering an untitled and uniciently simple or unsupported rules. [60] The Flexible Box Module has been improved and is much more straightforward and supported in all of the modern browsers. [66] Older browsers still have those issues, but most of those (mainly Internet Explorer 9 and below) are no longer supported by their vendors. [67]
Absence of expressions
There was no standard ability to specify property values ​​as simple expressions (such as margin-left: 10% – 3em + 4px;). This would be useful in a variety of cases, such as calculating the size of columns to a constraint on the sum of all columns. Internet Explorer versions 5 to 7 support a proprietary expression () statement, [68] with similar functionality. This proprietary expression () statement is no longer supported from Internet Explorer 8 onwards, except in compatibility modes. This decision was taken for “standards compliance, browser performance, and security reasons”. [68] However, a candidate recommendation with a calc () value to address this limitation has been published by the CSS WG [69]and has since been supported in all of the modern browsers. [70]
Lack of column declaration
Although possible in current CSS 3 (using the column-countmodule), [71] layouts with multiple columns can be complex to implement in CSS 2.1. With CSS 2.1, the process is often done using floating elements, which are often done by different browsers. All of the modern browsers support this CSS 3 feature in one form or another. [72]


Separation of content from presentation
Main article: Separation of presentation and content
CSS facilitates publication based on nominal parameters. Nominal parameters include explicit user preferences, different web browsers, the type of device being used to view the content (a desktop computer or mobile Internet device), the geographic location of the user and many other variables.
Site-wide consistency
Main article: Style sheet (web development)
When CSS is used effectively, in terms of inheritance and “cascading”, a global style sheet can be used to affect and style elements site-wide. If the situation should be changed or adjusted, these changes should be made in the global style sheet. Before CSS, this spell was more difficult, expensive and time-consuming.
A stylesheet, internal or external, specifies the style for a range of HTML elements selected by class, type or relationship to others. This is much more efficient than repeating style inline information for each instance of the element. An external stylesheet is usually stored in the browser cache , and can be used on multiple pages without being reloaded.
Reformatting page
Main article: Progressive enhancement
With a simple change of one line, a different style can be used for the same page. This provides advantages for accessibility, as well as providing the ability to tailor a page or site to different target devices. Furthermore, devices not able to understand the styling still display the content.
Without CSS, web designers must typically lay out their pages as they do not understand them (see Web Design # Accessibility ).



Main article: CSS framework

CSS frameworks are pre-prepared libraries That are Meant to allow for Easier, more standards-compliant styling of web pages using the Cascading Style Sheets language. CSS frameworks include Foundation , Blueprint , Bootstrap , Cascade Framework and Materialize. Like programming and scripting language libraries, CSS frameworks are usually incorporated as external.<head>. They provide a number of ready-made options for designing and laying out the web page. Although many of these frameworks have been published, some authors use them for rapid prototyping, or for learning from, and prefer to ‘handcraft’. in the site’s styling. [73]

Design methodologies

The size of CSS resources used in a project increases, a development team often needs to decide on a common design methodology to keep them organized. The goals are ease of development, ease of collaboration during development and performance of the deployed stylesheets in the browser. Popular methods include OOCSS – object oriented CSS, CSS – atomic CSS, CSS – organic Cascade Style Sheet, SMACSS – scalable and modular architecture for CSS and BEM – block, element, modify. [74]


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