css/css-backgrounds/animations/background-color-animation-with-mask.html

<!DOCTYPE html>
<html class="reftest-wait">
<link rel="help" href="https://drafts.csswg.org/css-backgrounds-3/#background-color">
<link rel="match" href="background-color-animation-with-mask-ref.html">
<style>
@keyframes blue-anim {
  0% { background-color: rgb(0, 0, 100); }
  100% { background-color: rgb(0, 0, 200); }
}
.container {
  width: 100px;
  height: 100px;
  -webkit-mask-image: url('../resources/stripes-100.png');
  -webkit-mask-size: 100px 100px;
  -webkit-mask-repeat: no-repeat;
  mask-image: url('../resources/stripes-100.png');
  mask-size: 100px 100px;
  mask-repeat: no-repeat;

  /* force animation to start effectively stalled at the midpoint */
  animation: blue-anim 10000s cubic-bezier(0, 1, 1, 0) -5000s;
}

</style>
<script src="/common/reftest-wait.js"></script>
<body>
  <div class="container"></div>
<script>
document.getAnimations()[0].ready.then(() => {
  takeScreenshot();
});
</script>
</body>
</html>