view-timeline-inset

Allowed values for view-timeline-inset are:

auto

If set, the corresponding scroll-padding (or equivalent longhand value) for that edge of the scrollport is used. If this is not set (or set to auto), the value will usually be 0, although some user agents may use heuristics to determine a different default value if appropriate.

<length-percentage>

Any valid <length-percentage> value is accepted as an inset/outset value.

• If the value is positive, the position of the animation's start/end will be moved inside the scrollport by the specified length or percentage.
• If the value is negative, the position of the animation's start/end will be moved outside the scrollport by the specified length or percentage, i.e. it will start animating before it appears in the scrollport, or finish animating after it leaves the scrollport.

If two values are provided, the first value represents the start inset/outset in the relevant axis (where the animation begins) and the second value represents the end inset/outset (where the animation ends). If only one value is provided, the start and end inset/outset are both set to the same value.

view-timeline-inset = 
  [ [ auto | <length-percentage> ]{1,2} ]#  

<length-percentage> = 
  <length>      |
  <percentage>  

A view progress timeline named --subjectReveal is defined using the view-timeline property on a subject element with a class of animation. This is then set as the timeline for the same element using animation-timeline: --subjectReveal;. The result is that the subject element animates as it moves upwards through the document as it is scrolled.

A view-timeline-inset declaration is also set to make the animation begin later than expected, and finish earlier.

HTML

The HTML for the example is shown below.

<div class="content">
  <h1>Content</h1>

  <p>
    Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod
    tempor incididunt ut labore et dolore magna aliqua. Risus quis varius quam
    quisque id. Et ligula ullamcorper malesuada proin libero nunc consequat
    interdum varius. Elit ullamcorper dignissim cras tincidunt lobortis feugiat
    vivamus at augue.
  </p>

  <p>
    Dolor sed viverra ipsum nunc aliquet. Sed sed risus pretium quam vulputate
    dignissim. Tortor aliquam nulla facilisi cras. A erat nam at lectus urna
    duis convallis convallis. Nibh ipsum consequat nisl vel pretium lectus.
    Sagittis aliquam malesuada bibendum arcu vitae elementum. Malesuada bibendum
    arcu vitae elementum curabitur vitae nunc sed velit.
  </p>

  <div class="subject animation"></div>

  <p>
    Adipiscing enim eu turpis egestas pretium aenean pharetra magna ac. Arcu
    cursus vitae congue mauris rhoncus aenean vel. Sit amet cursus sit amet
    dictum. Augue neque gravida in fermentum et. Gravida rutrum quisque non
    tellus orci ac auctor augue mauris. Risus quis varius quam quisque id diam
    vel quam elementum. Nibh praesent tristique magna sit amet purus gravida
    quis. Duis ultricies lacus sed turpis tincidunt id aliquet. In egestas erat
    imperdiet sed euismod nisi. Eget egestas purus viverra accumsan in nisl nisi
    scelerisque. Netus et malesuada fames ac.
  </p>
</div>

CSS

The subject element and its containing content element are styled minimally, and the text content is given some basic font settings:

.subject {
  width: 300px;
  height: 200px;
  margin: 0 auto;
  background-color: deeppink;
}

.content {
  width: 75%;
  max-width: 800px;
  margin: 0 auto;
}

p,
h1 {
  font-family: Arial, Helvetica, sans-serif;
}

h1 {
  font-size: 3rem;
}

p {
  font-size: 1.5rem;
  line-height: 1.5;
}

The <div> with the class of subject is also given a class of animation — this is where view-timeline is set to define a named view progress timeline. We also give it a view-timeline-inset declaration to make the animation begin later than expected, and finish earlier. It is also given an animation-timeline name with the same value to declare that this will be the element animated as the view progress timeline is progressed.

Last, an animation is specified on the element that animates its opacity and scale, causing it to fade in and size up as it moves up the scroller.

.animation {
  view-timeline: --subjectReveal block;
  view-timeline-inset: 70% -100px;
  animation-timeline: --subjectReveal;

  animation-name: appear;
  animation-fill-mode: both;
  animation-duration: 1ms; /* Firefox requires this to apply the animation */
}

@keyframes appear {
  from {
    opacity: 0;
    transform: scaleX(0);
  }

  to {
    opacity: 1,
    transform: scaleX(1);
  }
}

Result

Scroll to see the subject element being animated.

• animation-timeline
• timeline-scope
• view-timeline, view-timeline-axis, view-timeline-name
• CSS scroll-driven animations