none

When applied to a pseudo-element, the pseudo-element is not generated. If applied to an element, the value has no effect.

normal

Computes to none for the ::before and ::after pseudo-elements.

<string>

Specifies the "alt text" for the element. This value can be any number of text characters. Non-Latin characters must be encoded using their Unicode escape sequences: for example, \000A9 represents the copyright symbol.

<image>

An <image>, denoted by the url() or <gradient> data type, or part of the webpage, defined by the element() function, denoting the content to display.

counter()

The value of a CSS counter, generally a number produced by computations defined by <counter-reset> and <counter-increment> properties. It can be displayed using either the counter() or counters() function.

The counter() function has two forms: 'counter(name)' or 'counter(name, style)'. The generated text is the value of the innermost counter of the given name in scope at the given pseudo-element. It is formatted in the specified <list-style-type> (decimal by default).

The counters() function also has two forms: 'counters(name, string)' or 'counters(name, string, style)'. The generated text is the value of all counters with the given name in scope at the given pseudo-element, from outermost to innermost, separated by the specified string. The counters are rendered in the indicated <list-style-type> (decimal by default).

attr(x)

The value of the element's attribute x as a string. If there is no attribute x, an empty string is returned. The case-sensitivity of attribute names depends on the document language.

open-quote | close-quote

These values are replaced by the appropriate string from the quotes property.

no-open-quote | no-close-quote

Introduces no content, but increments (decrements) the level of nesting for quotes.

CSS-generated content is not included in the DOM. Because of this, it will not be represented in the accessibility tree and certain assistive technology/browser combinations will not announce it. If the content conveys information that is critical to understanding the page's purpose, it is better to include it in the main document.

• Accessibility support for CSS generated content – Tink
• Explanation of WCAG, Guideline 1.3 – MDN
• Understanding Success Criterion 1.3.1 | W3C Understanding WCAG 2.0

content = 
  normal                                              |
  none                                                |
  [ <content-replacement> | <content-list> ] [ / [ <string> | <counter> ]+ ]?  |
  element( )                                          

<content-replacement> = 
  <image>  

<content-list> = 
  [ <string> | contents | <image> | <counter> | <quote> | <target> | <leader()> ]+  

<counter> = 
  <counter()>   |
  <counters()>  

<image> = 
  <url>       |
  <gradient>  

<quote> = 
  open-quote      |
  close-quote     |
  no-open-quote   |
  no-close-quote  

<target> = 
  <target-counter()>   |
  <target-counters()>  |
  <target-text()>      

<leader()> = 
  leader( <leader-type> )  

<counter()> = 
  counter( <counter-name> , <counter-style>? )  

<counters()> = 
  counters( <counter-name> , <string> , <counter-style>? )  

<target-counter()> = 
  target-counter( [ <string> | <url> ] , <custom-ident> , <counter-style>? )  

<target-counters()> = 
  target-counters( [ <string> | <url> ] , <custom-ident> , <string> , <counter-style>? )  

<target-text()> = 
  target-text( [ <string> | <url> ] , [ content | before | after | first-letter ]? )  

<leader-type> = 
  dotted    |
  solid     |
  space     |
  <string>  

<counter-style> = 
  <counter-style-name>  |
  <symbols()>           

<symbols()> = 
  symbols( <symbols-type>? [ <string> | <image> ]+ )  

<symbols-type> = 
  cyclic      |
  numeric     |
  alphabetic  |
  symbolic    |
  fixed       

This example inserts quotation marks around quotes, and adds the word "Chapter" before headings.

HTML

<h1>5</h1>
<p>According to Sir Tim Berners-Lee,
  <q cite="http://www.w3.org/People/Berners-Lee/FAQ.html#Internet">I was
    lucky enough to invent the Web at the time when the Internet
    already existed - and had for a decade and a half.</q>
  We must understand that there is nothing fundamentally wrong
  with building on the contributions of others.
</p>

<h1>6</h1>
<p>According to the Mozilla Manifesto,
  <q cite="http://www.mozilla.org/en-US/about/manifesto/">Individuals
    must have the ability to shape the Internet and
    their own experiences on the Internet.</q>
  Therefore, we can infer that contributing to the open web
  can protect our own individual experiences on it.
</p>

CSS

q {
  color: blue;
}

q::before {
  content: open-quote;
}

q::after {
  content: close-quote;
}

h1::before {
  content: "Chapter ";  /* The trailing space creates separation
                           between the added content and the
                           rest of the content */
}

Result

This example inserts an image before the link. If the image is not found, it inserts text instead.

HTML

<a href="https://www.mozilla.org/en-US/">Mozilla Home Page</a>

CSS

a::before {
  content: url("https://mozorg.cdn.mozilla.net/media/img/favicon.ico") / " MOZILLA: ";
  font: x-small Arial, sans-serif;
  color: gray;
}

Result

This example inserts additional text after special items in a list.

HTML

<h2>Paperback Best Sellers</h2>
<ol>
  <li>Political Thriller</li>
  <li class="new-entry">Halloween Stories</li>
  <li>My Biography</li>
  <li class="new-entry">Vampire Romance</li>
</ol>

CSS

.new-entry::after {
  content: " New!";  /* The leading space creates separation
                        between the added content and the
                        rest of the content */
  color: red;
}

Result

This example inserts an image before each link, and adds its id attribute after.

HTML

<ul>
  <li><a id="moz" href="https://www.mozilla.org/">
    Mozilla Home Page</a></li>
  <li><a id="mdn" href="https://developer.mozilla.org/">
    Mozilla Developer Network</a></li>
</ul>

CSS

a {
  text-decoration: none;
  border-bottom: 3px dotted navy;
}

a::after {
  content: " (" attr(id) ")";
}

#moz::before {
  content: url("https://mozorg.cdn.mozilla.net/media/img/favicon.ico");
}

#mdn::before {
  content: url("mdn-favicon16.png");
}

li {
  margin: 1em;
}

Result

This example replaces an element's content with an image. You can replace the contents of an element with either a url() or an <image> value. Content added with ::before or ::after will not be generated as the contents of the element have been replaced.

HTML

<div id="replaced">Mozilla</div>

CSS

#replaced {
  content: url("mdn.svg");
}

#replaced::after { /* will not show if element replacement is supported */
  content: " (" attr(id) ")";
}

Result

• Replaced elements
• ::after
• ::before
• ::marker
• contain
• quotes
• url() function