This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the specification changes.

Summary

The animation CSS property is a shorthand property for animation-name, animation-duration, animation-timing-function, animation-delay, animation-iteration-count, animation-direction, animation-fill-mode and animation-play-state.

A description of which properties are animatable is available; it's worth noting that this description is also valid for CSS transitions.

Initial valueas each of the properties of the shorthand:
Applies toall elements, ::before and ::after pseudo-elements
Inheritedno
Mediavisual
Computed valueas each of the properties of the shorthand:
Animation typediscrete
Canonical orderorder of appearance in the formal grammar of the values

Syntax

/* @keyframes duration | timing-function | delay | 
   iteration-count | direction | fill-mode | play-state | name */
  animation: 3s ease-in 1s 2 reverse both paused slidein;

/* @keyframes duration | timing-function | delay | name */
  animation: 3s linear 1s slidein;

/* @keyframes duration | name */
  animation: 3s slidein;

The order is important within each animation definition: the first value that can be parsed as a <time> is assigned to the animation-duration, and the second one is assigned to animation-delay.

Note that order is also important within each animation definition for distinguishing animation-name values from other keywords. When parsing, keywords that are valid for properties other than animation-name whose values were not found earlier in the shorthand must be accepted for those properties rather than for animation-name. Furthermore, when serializing, default values of other properties must be output in at least the cases necessary to distinguish an animation-name that could be a value of another property, and may be output in additional cases.

Formal syntax

<single-animation>#

where
<single-animation> = <time> || <single-timing-function> || <time> || <single-animation-iteration-count> || <single-animation-direction> || <single-animation-fill-mode> || <single-animation-play-state> || [ none | <keyframes-name> ]

where
<single-timing-function> = <single-transition-timing-function>
<single-animation-iteration-count> = infinite | <number>
<single-animation-direction> = normal | reverse | alternate | alternate-reverse
<single-animation-fill-mode> = none | forwards | backwards | both
<single-animation-play-state> = running | paused
<keyframes-name> = <custom-ident> | <string>

where
<single-transition-timing-function> = ease | linear | ease-in | ease-out | ease-in-out | step-start | step-end | steps( <integer> [, [ start | end ] ]? ) | cubic-bezier( <number>, <number>, <number>, <number> )

Examples

See CSS animations for examples.

Cylon Eye

Considering all browser-specific prefixes, here is a cylon eye animation incorporating linear gradients and animations that works across all major browsers:

<div class="view_port">
  <div class="polling_message">
    Listening for dispatches
  </div>
  <div class="cylon_eye"></div>
</div>
.polling_message {
  color: white;
  float: left;
  margin-right: 2%;            
}

.view_port {
  background-color: black;
  height: 25px;
  width: 100%;
  overflow: hidden;
}

.cylon_eye {
  background-color: red;
  background-image: -webkit-linear-gradient(    left, rgba( 0,0,0,0.9 ) 25%, rgba( 0,0,0,0.1 ) 50%, rgba( 0,0,0,0.9 ) 75%);
  background-image:    -moz-linear-gradient(    left, rgba( 0,0,0,0.9 ) 25%, rgba( 0,0,0,0.1 ) 50%, rgba( 0,0,0,0.9 ) 75%);
  background-image:      -o-linear-gradient(    left, rgba( 0,0,0,0.9 ) 25%, rgba( 0,0,0,0.1 ) 50%, rgba( 0,0,0,0.9 ) 75%);
  background-image:         linear-gradient(to right, rgba( 0,0,0,0.9 ) 25%, rgba( 0,0,0,0.1 ) 50%, rgba( 0,0,0,0.9 ) 75%);
  color: white;
  height: 100%;
  width: 20%;

  -webkit-animation: 4s linear 0s infinite alternate move_eye;
     -moz-animation: 4s linear 0s infinite alternate move_eye;
       -o-animation: 4s linear 0s infinite alternate move_eye;
          animation: 4s linear 0s infinite alternate move_eye;
}

@-webkit-keyframes move_eye { from { margin-left:-20%; } to { margin-left:100%; }  }
   @-moz-keyframes move_eye { from { margin-left:-20%; } to { margin-left:100%; }  }
     @-o-keyframes move_eye { from { margin-left:-20%; } to { margin-left:100%; }  }
        @keyframes move_eye { from { margin-left:-20%; } to { margin-left:100%; }  }

Specifications

Specification Status Comment
CSS Animations
The definition of 'animation' in that specification.
Working Draft Initial definition

Browser compatibility

Feature Chrome Edge Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support (Yes)-webkit
43.0
(Yes) 5.0 (5.0)-moz
16.0 (16.0)[2]
10 12-o
12.50[3]
4.0-webkit
Feature Android Edge Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support 2.1 -webkit [1]
4.0 -webkit
(Yes) 5.0 (5.0)-moz
16.0 (16.0)
? ? (Yes)-webkit

[1] Partial support: animation-fill-mode property is not supported in Android browser below 2.3.

[2] In addition to the unprefixed support, Gecko 44.0 (Firefox 44.0 / Thunderbird 44.0 / SeaMonkey 2.41) added support for a -webkit prefixed version of the property for web compatibility reasons behind the preference layout.css.prefixes.webkit, defaulting to false. Since Gecko 49.0 (Firefox 49.0 / Thunderbird 49.0 / SeaMonkey 2.46) the preference defaults to true.

[3] See the release notes to Opera 12.50.

See also