JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flex-column" style="height: 100%">
  <div style="background-color: red">
    Foo
  </div>
  <div class="flex-column flex-shrink1">
    <div class="flex-column flex-shrink1" style="overflow-y: scroll; background-color: green">
      Bar<br>Bar<br>Bar<br>Bar<br>
      Bar<br>Bar<br>Bar<br>Bar<br>
      Bar<br>Bar<br>Bar<br>Bar<br>
      Bar<br>Bar<br>Bar<br>Bar<br>
    </div>
  </div>
</div>

CSS

html, body {
    height: 100%;
    padding: 0px;
    margin: 0px;
}

.flex-column {
    display: flex;
    flex-direction: column;
}

.flex-column>* {
    flex-shrink: 0;
}

.flex-shrink1 {
    flex-shrink: 1;
}