css/css-view-transitions/content-with-transparent-background-ref.html

<!DOCTYPE html>
<title>View transitions: element with transparent background (ref)</title>
<link rel="help" href="https://drafts.csswg.org/css-view-transitions-1/">
<link rel="author" href="mailto:khushalsagar@chromium.org">
<style>
.target {
  width: 100px;
  height: 100px;
  view-transition-name: target;
  position: fixed;
  top: 25px;
  left: 25px;
  background: rgba(0,0,0,0);
}

.embedded {
  width: 25%;
  height: 50%;
  position: absolute;
  top: 0px;
  will-change: opacity;
}

#one{
  left: 25%;
  background: lightblue;
}
#two {
  left: 50%;
  background: lightgreen;
}

html::view-transition-group(hidden) { animation-duration: 300s; }
html::view-transition-image-pair(hidden) { animation: unset; opacity: 0; }

html::view-transition-group(target) { animation: unset; }
html::view-transition-old(target) { animation: unset; opacity: 1; }
html::view-transition-new(target) { animation: unset; opacity: 0; }

</style>
<div class="target">
  <div class="embedded" id="one"></div>
  <div class="embedded" id="two"></div>
</div>