animation

This property is a shorthand for the following CSS properties:

• animation-delay
• animation-direction
• animation-duration
• animation-fill-mode
• animation-iteration-count
• animation-name
• animation-play-state
• animation-timeline
• animation-timing-function

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

/* @keyframes duration | easing-function | delay | name */
animation: 3s linear 1s slide-in;

/* two animations */
animation:
  3s linear slide-in,
  3s ease-out 5s slide-out;

The animation property is specified as one or more single animations, separated by commas.

Each individual animation is specified as:

• zero, one, or two occurrences of the <time> value

• zero or one occurrences of the following values:

  • <single-easing-function>
  • <single-animation-iteration-count>
  • <single-animation-direction>
  • <single-animation-fill-mode>
  • <single-animation-play-state>

• an optional name for the animation, which may be none, a <custom-ident>, or a <string>

<single-easing-function>

Determines the type of transition. The value must be one of those available in <easing-function>.

<single-animation-iteration-count>

The number of times the animation is played. The value must be one of those available in animation-iteration-count.

<single-animation-direction>

The direction in which the animation is played. The value must be one of those available in animation-direction.

<single-animation-fill-mode>

Determines how styles should be applied to the animation's target before and after its execution. The value must be one of those available in animation-fill-mode.

<single-animation-play-state>

Determines whether the animation is playing or not. The value must be one of those available in animation-play-state.

The order of time values within each animation definition is important: 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.

The order of other values within each animation definition is also important for distinguishing an animation-name value from other values. If a value in the animation shorthand can be parsed as a value for an animation property other than animation-name, then the value will be applied to that property first and not to animation-name. For this reason, the recommended practice is to specify a value for animation-name as the last value in a list of values when using the animation shorthand; this holds true even when you specify multiple, comma-separated animations using the animation shorthand.

While an animation name must be set for an animation to be applied, all values of the animation shorthand are optional, and default to the initial value for each long-hand animation component. The initial value of animation-name is none, meaning if no animation-name value is declared in the animation shorthand property, there is no animation to apply on any of the properties.

When the animation-duration value is omitted from the animation shorthand property, the value for this property defaults to 0s. In this case, the animation will still occur (the animationStart and animationEnd events will be fired) but no animation will be visible.

In the case of the animation-fill-mode forwards value, animated properties behave as if included in a set will-change property value. If a new stacking context is created during the animation, the target element retains the stacking context after the animation has finished.

Blinking and flashing animation can be problematic for people with cognitive concerns such as Attention Deficit Hyperactivity Disorder (ADHD). Additionally, certain kinds of motion can be a trigger for Vestibular disorders, epilepsy, and migraine and Scotopic sensitivity.

Consider providing a mechanism for pausing or disabling animation as well as using the Reduced Motion Media Query to create a complimentary experience for users who have expressed a preference for reduced animated experiences.

• Designing Safer Web Animation For Motion Sensitivity · An A List Apart Article
• An Introduction to the Reduced Motion Media Query | CSS-Tricks
• Responsive Design for Motion | WebKit
• MDN Understanding WCAG, Guideline 2.2 explanations
• Understanding Success Criterion 2.2.2 | W3C Understanding WCAG 2.0

animation = 
  <single-animation>#  

<single-animation> = 
  <time [0s,∞]>                       ||
  <easing-function>                   ||
  <time>                              ||
  <single-animation-iteration-count>  ||
  <single-animation-direction>        ||
  <single-animation-fill-mode>        ||
  <single-animation-play-state>       ||
  [ none | <keyframes-name> ]         

<easing-function> = 
  <linear-easing-function>        |
  <cubic-bezier-easing-function>  |
  <step-easing-function>          

<single-animation-iteration-count> = 
  infinite        |
  <number [0,∞]>  

<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>        

<linear-easing-function> = 
  linear      |
  <linear()>  

<cubic-bezier-easing-function> = 
  ease              |
  ease-in           |
  ease-out          |
  ease-in-out       |
  <cubic-bezier()>  

<step-easing-function> = 
  step-start  |
  step-end    |
  <steps()>   

<linear()> = 
  linear( [ <number> && <percentage>{0,2} ]# )  

<cubic-bezier()> = 
  cubic-bezier( [ <number [0,1]> , <number> ]#{2} )  

<steps()> = 
  steps( <integer> , <step-position>? )  

<step-position> = 
  jump-start  |
  jump-end    |
  jump-none   |
  jump-both   |
  start       |
  end         

Here we animate a yellow sun across a light blue sky. The sun rises to the center of the viewport and then falls out of sight.

<div class="sun"></div>

:root {
  overflow: hidden; /* hides any part of the sun below the horizon */
  background-color: lightblue;
  display: flex;
  justify-content: center; /* centers the sun in the background */
}

.sun {
  background-color: yellow;
  border-radius: 50%; /* creates a circular background */
  height: 100vh; /* makes the sun the size of the viewport */
  aspect-ratio: 1 / 1;
  animation: 4s linear 0s infinite alternate sun-rise;
}

@keyframes sun-rise {
  from {
    /* pushes the sun down past the viewport */
    transform: translateY(110vh);
  }
  to {
    /* returns the sun to its default position */
    transform: translateY(0);
  }
}

Adding onto the sun animation in the previous example, we add a second animation changing the color of the sun as it rises and sets. The sun starts off dark red when it is below the horizon and changes to a bright orange as it reaches the top.

<div class="sun"></div>

:root {
  overflow: hidden;
  background-color: lightblue;
  display: flex;
  justify-content: center;
}

.sun {
  background-color: yellow;
  border-radius: 50%;
  height: 100vh;
  aspect-ratio: 1 / 1;
  animation: 4s linear 0s infinite alternate animating-multiple-properties;
}

/* it is possible to animate multiple properties in a single animation */
@keyframes animating-multiple-properties {
  from {
    transform: translateY(110vh);
    background-color: red;
    filter: brightness(75%);
  }
  to {
    transform: translateY(0);
    background-color: orange;
    /* unset properties i.e. 'filter' will revert to default values */
  }
}

Here is a sun that rises and falls on a lightblue background. The sun gradually rotates through a rainbow of colors. The timing of the sun's position and color are independent.

<div class="sun"></div>

:root {
  overflow: hidden;
  background-color: lightblue;
  display: flex;
  justify-content: center;
}

.sun {
  background-color: yellow;
  border-radius: 50%;
  height: 100vh;
  aspect-ratio: 1 / 1;
  /* multiple animations are separated by commas, each animation's parameters are set independently */
  animation:
    4s linear 0s infinite alternate rise,
    24s linear 0s infinite psychedelic;
}

@keyframes rise {
  from {
    transform: translateY(110vh);
  }
  to {
    transform: translateY(0);
  }
}

@keyframes psychedelic {
  from {
    filter: hue-rotate(0deg);
  }
  to {
    filter: hue-rotate(360deg);
  }
}

Here is a yellow sun on a lightblue background. The sun bounces between the left and right sides of the viewport. The sun remains in the viewport even though a rise animation is defined. The rise animation's transform property is 'overwritten' by the bounce animation.

<div class="sun"></div>

:root {
  overflow: hidden;
  background-color: lightblue;
  display: flex;
  justify-content: center;
}

.sun {
  background-color: yellow;
  border-radius: 50%;
  height: 100vh;
  aspect-ratio: 1 / 1;
  /*
    animations declared later in the cascade will override the
    properties of previously declared animations
  */
  /* bounce 'overwrites' the transform set by rise, hence the sun only moves horizontally */
  animation:
    4s linear 0s infinite alternate rise,
    4s linear 0s infinite alternate bounce;
}

@keyframes rise {
  from {
    transform: translateY(110vh);
  }
  to {
    transform: translateY(0);
  }
}

@keyframes bounce {
  from {
    transform: translateX(-50vw);
  }
  to {
    transform: translateX(50vw);
  }
}

See Using CSS animations for additional examples.

• Using CSS animations
• JavaScript AnimationEvent API