<!DOCTYPE html>
<html class="reftest-wait">
<style>
@keyframes anim {
  from { background-color: rgb(255, 255, 255); }
  to { background-color: rgb(255, 255, 255); }
}
#target::before {
  content: 'initial';
  background-color: rgb(0, 0, 0);
  height: 100px;
  width: 100px;
  position: absolute;
}
#target.hover::before{
  content: '';
  animation: anim 100s steps(1, start);
}
</style>
<div id="target"></div>
<script>
window.addEventListener("load", () => {
  target.className = 'hover';
  target.addEventListener('animationstart', () => {
    document.documentElement.classList.remove('reftest-wait');
  });
});
</script>
</html>