JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
  <div id="flexible">
    content
    content
    content
  </div>
  <div id="popup">
    content
    content
  </div>
  <div id="footer">
    I am a footer
  </div>
</div>

CSS

#container {
  height: 100%;
  width: 100%;
}

#flexible {
  
}

#popup {
  max-height: 20%;
  min-height: 10%;
  position: absolute;
  bottom: 0;
  margin-bottom: 50px;
  background-color: #cccccc;
}

#footer {
  height: 50px;
  background-color: #666666;
  position: absolute;
  bottom: 0;
}