Как сделать липкий элемент «плавать»

#root-container {
  display: flex;
}

#container1 {
  width: 100px;
  height: 500px;
  background-color: grey;
}

#sticky-container {
  width: 320px;
  max-height: 500px;
  position: relative;
  background-color: lightgrey;
}

#sticky-container-header {
  width: 320px;
  height: 100px;
  background-color: #2f4d92;
}

#full-height-content {
  width: 100%;
  height: 400px;
  overflow-y: scroll;
  background-color: #d67e23;
  margin-top:-20px; /*same as the margin-bottom*/
}

#sticky-content {
  width: 80%;
  height: 100px;
  margin-top:-100px; /*same as height*/
  margin-bottom:20px; /*to avoid going under the bottom:20px we want*/
  position: sticky;
  top:calc(100vh - 100px - 20px);
  background-color: rgba(0,0,0,0.5);
}

#bottom {
  width: 420px;
  height: 100px;
  background-color: purple;
}

body {
  margin:0;
}

<div id='root-container'>
  <div id="container1"></div>
  <div id="sticky-container">
    <div id='sticky-container-header'></div>
    <div id='sticky-content'></div>
    <div id='full-height-content'>
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    </div>
  </div>
</div>
<div id="bottom">
</div>