Using CSS generated content
This article describes some ways in which you can use CSS to add content when a document is displayed. You modify your stylesheet to add text content or images.
One of the important advantages of CSS is that it helps you to separate a document’s style from its content. However, there are situations where it makes sense to specify certain content as part of the stylesheet, not as part of the document. You can specify text or image content within a stylesheet when that content is closely linked to the document’s structure.
Note: Content specified in a stylesheet does not become part of the DOM.
Specifying content in a stylesheet can cause complications. For example, you might have different language versions of your document that share a stylesheet. If you specify content in your stylesheet that requires translation, you have to put those parts of your stylesheet in different files and arrange for them to be linked with the appropriate language versions of your document.
This issue does not arise if the content you specify consists of symbols or images that apply in all languages and cultures.
Examples
Text content
CSS can insert text content before or after an element, or change the content of a list item marker (such as a bullet symbol or number) before a or other element with display: list-item; . To specify this, make a rule and add ::before , ::after , or ::marker to the selector. In the declaration, specify the content property with the text content as its value.
HTML
span class="ref">somethingspan>
CSS
.ref::before font-weight: bold; color: navy; content: "Reference "; > Output
The character set of a stylesheet is UTF-8 by default, but it can also be specified in the link, in the stylesheet itself, or in other ways. For details, see 4.4 CSS style sheet representation in the CSS Specification.
Individual characters can also be specified by an escape mechanism that uses backslash as the escape character. For example, «\265B» is the chess symbol for a black queen ♛. For details, see Referring to characters not represented in a character encoding and Characters and case in the CSS Specification.
Image content
To add an image before or after an element, you can specify the URL of an image file in the value of the content property.
This rule adds a space and an icon after every link that has the class glossary :
HTML
a href="developer.mozilla.org" class="glossary">developer.mozilla.orga>
CSS
a.glossary::after content: " " url("glossary-icon.gif"); > Found a content problem with this page?
This page was last modified on Jun 30, 2023 by MDN contributors.
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CSS Content
CSS has a property called content. It can only be used with the pseudo-elements ::after and ::before. It is written like a pseudo selector (with the colon), but it’s called a pseudo-element because it’s not actually selecting anything that exists on the page but adding something new to the page. This is what it looks like:
And the output would be like: • Email address: [email protected] Maybe that example doesn’t get you drooling, but pseudo-element content can be quite useful and do cool things. Let’s go through some ideas and considerations.
Hey! That’s content not design!
The first concern might be that of a separation-between-content-and-design purist. You are literally adding text content to the page with CSS content, and that breaks that barrier. The spec is done and the idea implemented, but that doesn’t mean it’s not worth discussing. If you have an opinion about CSS content and its use, please share in the comments. I think it’s awesome and perfectly suited for CSS. Consider the example above where we preface all elements with a class of email-address with the text “Email address: “. That is a design decision, where for the clarity of content, it was decided that having that text before email addresses made the content more clear. Perhaps in a redesign of the site, there was less room where those email addresses are being displayed and it was decided that instead of prefacing them with text, a small icon would be used instead. This fits with the idea of CSS, in that the HTML content doesn’t need to change at all, this change could be solely accomplished with CSS. I’m going to publish an article tomorrow with this kind of idea.
If you need to use a special character in the CSS content, it’s kinda weird. How I do it is I figure out what the ASCII number is for the symbol. This chart of glyphs is handy. So on that chart the copyright © symbol is © – so the ASCII number is 169. Then I drop that number in the Entity Conversion Calculator which will convert it into what you need for CSS. Here’s some random useful ones: \2018 – Left Single Smart Quote
\2019 – Right Single Smart Quote
\00A9 – Copyright
\2713 – Checkmark
\2192 – Right arrow
\2190 – Left arrow
Example Trick: Checkmark visited links
#main-content a:visited::before
You are able to insert attributes of the elements you are targeting as content. For example, an anchor link might have a title attribute:
Any attribute can be targeted as such, in the format attr(name-of-attribute). If you’d like to insert something into the HTML to use for a CSS content purpose (but nothing else), you could use the new data- attribute prefix in HTML5.
Example Trick: CSS3 tooltips
a < color: #900; text-decoration: none; >a:hover < color: red; position: relative; >a[title]:hover::after
This example uses the title attribute, and other examples like this that you find around the web also use the title attribute. It’s probably the correct one to use. However, do note that browsers have their own tooltip popups that they do. When that comes up, it will cover this, and look weird. I tried to take a screenshot of the issue but there it wasn’t letting me for some reason. There is no way to suppress this, other than just not using the title attribute. HTML5 data- attributes, again, could be useful here.
- Firebug can’t yet target pseduo elements. The web inspector in WebKit browsers can target them, but don’t show their property/values. I heard the IE dev tools could target them too, but not sure about the property/values.
- In WebKit, they have to be block level to be rotated. Firefox can rotate inline elements/pseudo-elements.
- In Firefox 3.0, pseudo elements can’t be absolutely positioned.
- They cannot be transitioned or animated.
Example Trick: Fancy email link popouts
I had an idea I wanted to try where you would have a vertical list of names, and as you moused over them, their email addresses would slide out from underneath them. To have the HTML be as clean as possible, I thought it would be cool to use the an ::after pseudo-element and a -webkit-transition to make it happen. But, alas, you cannot animate or transition a pseudo-element.
Using the ::after /content method, I got an example working it just doesn’t slide out like I thought would be cool. Using s I got the idea working, also in the demo page.
Example trick: display full links in print stylesheets
Browser support / Accessibility
All the major browsers (Firefox 3+, Safari 3+, Chrome 3+, Opera 10+, and Internet Explorer 8+) (See the full chart) support CSS content with the ::after/::before pseudo-elements and the spec is in its full candidate recommendation status.
Regarding accessibility, I’m just not 100% sure what the situation was. I was trying to use VoiceOver with Safari on my Mac with the email popout links demo. For best accessibility, I would think the goal would be to get it to read the whole text, including the CSS content being added. I had trouble getting it to do that, but I thought I did get it to do it once somehow. I was really bad at using VoiceOver and found it frustrating to get it to do what I was trying to do even at the most basic levels. If someone knows more about accessibility as it relates to CSS content, I’m sure we’d all love to know more.