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ამასთან, შეგიძლიათ იხილოთ სტატიის English (US) ვერსია.

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.

Syntax

/* 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.

Examples

Adding quotation marks

One simple example of using ::before pseudo-elements is to provide quotation marks. Here we use both ::before and ::after to insert quotation characters.

HTML

<q>Some quotes,</q> he said, <q>are better than none.</q>

CSS

q::before { 
  content: "«";
  color: blue;
}

q::after { 
  content: "»";
  color: red;
}

Result

Decorative example

We can style text or images in the content property almost any way we want.

HTML

<span class="ribbon">Notice where the orange box is.</span>

CSS

.ribbon {
  background-color: #5BC8F7;
}

.ribbon::before {
  content: "Look at this orange box.";
  background-color: #FFBA10;
  border-color: black;
  border-style: dotted;
}

Result

To-do list

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.

HTML

<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>

CSS

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;
}

JavaScript

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.

Result

Notes

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!)

HTML

<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>

CSS

#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;
}

Result

Specifications

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

Browser compatibility

FeatureChromeEdgeFirefoxInternet ExplorerOperaSafari
Basic support

Yes

Yes1

Yes

Yes1

1.52 3

11

9

81

7

41

4

41

Animation and transition support26 Yes4 No No No
FeatureAndroid webviewChrome for AndroidEdge mobileFirefox for AndroidOpera AndroidiOS SafariSamsung Internet
Basic support

Yes

Yes1

Yes

Yes1

Yes

Yes1

Yes

Yes1

?5.1 Yes
Animation and transition support Yes Yes Yes4 No No Yes

1. Supported as :before.

2. Before Firefox 57, Firefox had a bug where ::before pseudo-elements were still generated, even if the content property value were set to normal or none.

3. Before Firefox 3.5, only the CSS level 2 behavior of :before was supported, which disallowed position, float, list-style-* and some display properties.

See also

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ბოლო განახლების ავტორი: SphinxKnight,