JSFiddle - React, Tailwind, and code Playground

HTML

<section>
  <header>
    header: sized to content
    <br>(but is it really?)
  </header>
  <div>
    main content: fills remaining space<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
    x<br>x<br>x<br>x<br>x<br>x<br>x<br>x<br>
  </div>
  <footer>
    footer: fixed height in px
  </footer>
</section>

CSS

section {
  height: 300px;
  display: flex;
  flex-direction : column;
}
header {
  background: tomato;
}
div {
  flex: 1; /* or flex-grow: 1  */;
  overflow-x: auto;
  background: gold;
}
footer {
  background: lightgreen;
  min-height: 60px;
}