<!DOCTYPE html>
<html>
<head>
<style>
div {
  width: 100%;
  height: 200px;
}

.inner {
  width: 100px;
  height: 100px;
  background-color: green;
  right: 0px;
}

.fixedCB {
  filter: blur(0px);
}

.absCB {
  position: absolute;
}

.fixed {
  position: fixed;
}

.abs {
  position: absolute;
  top: 100px;
}

</style>
</head>
<body>
<div class="fixedCB">
  <div class="absCB" style="width:500px">
    <span id="mutate">
      Text content to give some width
      <div class="inner fixed"></div>
      <div class="inner abs"></div>
    </span>
  </div>
</div>

</body>
<script>
document.body.offsetHeight;
mutate.classList.add("fixedCB");
document.body.offsetHeight;
</script>
</html>