none

The animation is not associated with a timeline.

auto

The animation's timeline is the document's default DocumentTimeline.

scroll() Experimental

The "anonymous" timeline is provided by some ancestor of the current element.

See scroll() for additional information.

<timeline-name>

A <custom-ident> or string identifying the named scroll timeline, declared with the scroll-timeline-name property (or scroll-timeline shorthand property). If two or more scroll timelines share the same name, the last declared within the cascade will be used. If no matching scroll timeline is found, the animation is not associated with a timeline.

animation-timeline = 
  <single-animation-timeline>#  

<single-animation-timeline> = 
  auto             |
  none             |
  <timeline-name>  

<timeline-name> = 
  <custom-ident>  |
  <string>        

A scroll timeline named squareTimeline is defined using the scroll-timeline-name property on the element with id container. This is then applied to the animation on the #square element using animation-timeline: squareTimeline.

HTML

The HTML for the example is shown below.

<div id="container">
  <div id="square"></div>
  <div id="stretcher"></div>
</div>

CSS

The CSS for the container sets it as the source of a scroll timeline named squareTimeline using the scroll-timeline-name property (we could also set which scrollbar axis to use with scroll-timeline-axis, but there will be only one scrollbar here, and it will be used by default).

The height of the container is set to 300px and we also set the container to create a vertical scrollbar if it overflows (below we will use CSS on the "stretcher" element to ensure that it does overflow).

#container {
  height: 300px;
  overflow-y: scroll;
  scroll-timeline-name: squareTimeline;
  position: relative;
}

The CSS below defines a square that rotates in alternate directions according to the timeline provided by the animation-timeline property, which is set to the squareTimeline timeline named above.

#square {
  background-color: deeppink;
  width: 100px;
  height: 100px;
  margin-top: 100px;
  animation-name: rotateAnimation;
  animation-duration: 3s;
  animation-direction: alternate;
  animation-timeline: squareTimeline;

  position: absolute;
  bottom: 0;
}

@keyframes rotateAnimation {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }
}

The "stretcher" CSS simply sets the block height to 600px, which forces the container element to overflow and create scroll bars. Without this element there would be no scrollbar, and hence no scroll timeline to associate with the animation timeline.

#stretcher {
  height: 600px;
}

Result

Scroll to see the square element being animated.

The #square element is animated using an anonymous scrollbar timeline, which is applied to the element to be animated using the scroll() functional notation. The timeline in this particular example is provided by the nearest parent element that has (any) scrollbar, from the scrollbar in the block direction.

HTML

The HTML for the example is shown below.

<div id="container">
  <div id="square"></div>
  <div id="stretcher"></div>
</div>

CSS

The CSS below defines a square that rotates in alternate directions according to the timeline provided by the animation-timeline property. In this case the timeline is provided by scroll(block nearest), which means that it will select the scrollbar in the block direction of the nearest ancestor element that has scrollbars; in this case the vertical scrollbar of the "container" element.

Note that the block nearest options below are actually the default, so we could instead just have had: scroll().

#square {
  background-color: deeppink;
  width: 100px;
  height: 100px;
  margin-top: 100px;
  position: absolute;
  bottom: 0;

  animation-name: rotateAnimation;
  animation-duration: 3s;
  animation-direction: alternate;
  animation-timeline: scroll(block nearest);
}

@keyframes rotateAnimation {
  from {
    transform: rotate(0deg);
  }
  to {
    transform: rotate(360deg);
  }
}

The CSS for the container sets its height to 300px and we also set the container to create a vertical scrollbar if it overflows. The "stretcher" CSS sets the block height to 600px, which forces the container element to overflow. These two together ensure that the container has a vertical scrollbar, which allows it to be used as the source of the anonymous scrollbar timeline.

#container {
  height: 300px;
  overflow-y: scroll;
  position: relative;
}

#stretcher {
  height: 600px;
}

Result

Scroll to see the square element being animated.

• Using CSS animations
• Other related animation properties: animation, animation-composition, animation-delay, animation-direction, animation-duration, animation-fill-mode, animation-iteration-count, animation-name, animation-play-state, animation-timing-function