#composited-background {
  width: 100%;
  height: 100%;
  will-change: transform;
}

#container {
  position: relative;
  width: 400px;
  height: 60px;
  border: 1px solid black;
}

#composited-overlap-child {
  position: absolute;
  left: 0;
  bottom: 0px;
  width: 100%;
  height: 60px;
  background-color: orange;
}