<!DOCTYPE html>
<title>
Transform animation generates a containing block for fixed-pos descendants
even if the animation value is 'transform:none'
</title>
<style>
#parent {
  visibility: hidden;
  animation: anim 100s step-end;
}

#fixed {
  position: fixed;
  background-color: green;
  height: 100px;
  width: 100px;
}

#scroll {
  overflow-y: scroll;
  overflow-x: hidden;
  height: 80px;
  width: 100px;
}
@keyframes anim {
  0% { transform: none; }
  100% { transform: translateX(0px); }
}
</style>
<div id="scroll">
  <div id="parent">
    <div id="fixed"></div>
  </div>
</div>