In CSS, ::before
creates a pseudo-element that is the first child of the selected element. It is often used to add cosmetic content to an element with the content
property. It is inline by default.
/* Add a heart before links */ a::before { content: "♥"; }
Note: The pseudo-elements generated by ::before
and ::after
are contained by the element's formatting box, and thus don't apply to replaced elements such as <img>
, or to <br>
elements.
/* CSS3 syntax */ ::before /* CSS2 syntax */ :before
Note: CSS3 introduced the ::before
notation (with two colons) to distinguish pseudo-classes from pseudo-elements. Browsers also accept :before
, introduced in CSS2.
One simple example of using ::before
pseudo-elements is to provide quotation marks. Here we use both ::before
and
to insert quotation characters.::after
<q>Some quotes,</q> he said, <q>are better than none.</q>
q::before { content: "«"; color: blue; } q::after { content: "»"; color: red; }
We can style text or images in the content
property almost any way we want.
<span class="ribbon">Notice where the orange box is.</span>
.ribbon { background-color: #5BC8F7; } .ribbon::before { content: "Look at this orange box."; background-color: #FFBA10; border-color: black; border-style: dotted; }
In this example we will create a simple to-do list using pseudo-elements. This method can often be used to add small touches to the UI and improve user experience.
<ul> <li>Buy milk</li> <li>Take the dog for a walk</li> <li>Exercise</li> <li>Write code</li> <li>Play music</li> <li>Relax</li> </ul>
li { list-style-type: none; position: relative; margin: 2px; padding: 0.5em 0.5em 0.5em 2em; background: lightgrey; font-family: sans-serif; } li.done { background: #CCFF99; } li.done::before { content: ''; position: absolute; border-color: #009933; border-style: solid; border-width: 0 0.3em 0.25em 0; height: 1em; top: 1.3em; left: 0.6em; margin-top: -1em; transform: rotate(45deg); width: 0.5em; }
var list = document.querySelector('ul'); list.addEventListener('click', function(ev) { if( ev.target.tagName === 'LI') { ev.target.classList.toggle('done'); } }, false);
Here is the above code example running live. Note that there are no icons used, and the check-mark is actually the ::before
that has been styled in CSS. Go ahead and get some stuff done.
Although the positioning fixes in Firefox 3.5 do not allow content to be generated as a separate previous sibling (as per the CSS spec stating "The :before and :after pseudo-elements elements interact with other boxes... as if they were real elements inserted just inside their associated element."), they can be used to provide a slight improvement on tableless layouts (e.g., to achieve centering) in that, as long as the content to be centered is wrapped in a further child, a column before and after the content can be introduced without adding a previous or following sibling (i.e., it is perhaps more semantically correct to add an additional span as below, than it would to add an empty <div/> before and after). (And always remember to add a width to a float, since, otherwise, it will not float!)
<div class="example"> <span id="floatme">"Floated Before" should be generated on the left of the viewport and not allow overflow in this line to flow under it. Likewise should "Floated After" appear on the right of the viewport and not allow this line to flow under it.</span> </div>
#floatme { float: left; width: 50%; } /* To get an empty column, just indicate a hex code for a non-breaking space: \a0 as the content (use \0000a0 when following such a space with other characters) */ .example::before { content: "Floated Before"; float: left; width: 25% } .example::after { content: "Floated After"; float: right; width:25% } /* For styling */ .example::before, .example::after { background: yellow; color: red; }
Specification | Status | Comment |
---|---|---|
CSS Pseudo-Elements Level 4 The definition of '::before' in that specification. | Working Draft | No significant changes to the previous specification. |
CSS Transitions | Working Draft | Allows transitions on properties defined on pseudo-elements. |
CSS Animations | Working Draft | Allows animations on properties defined on pseudo-elements. |
Selectors Level 3 The definition of '::before' in that specification. | Recommendation | Introduces the two-colon syntax. |
CSS Level 2 (Revision 1) The definition of '::before' in that specification. | Recommendation | Initial definition, using the one-colon syntax |
Desktop | ||||||
---|---|---|---|---|---|---|
Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | |
Basic support | Yes
|
Yes
|
1.5
|
9
|
7
|
4
|
Animation and transition support | 26 | Yes | 4 | No | No | No |
Mobile | |||||||
---|---|---|---|---|---|---|---|
Android webview | Chrome for Android | Edge Mobile | Firefox for Android | Opera for Android | iOS Safari | Samsung Internet | |
Basic support | Yes
|
Yes
|
Yes
|
Yes
|
? | 5.1 | Yes |
Animation and transition support | Yes | Yes | Yes | 4 | No | No | Yes |
© 2005–2018 Mozilla Developer Network and individual contributors.
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-US/docs/Web/CSS/::before