JSFiddle - React, Tailwind, and code Playground

HTML

<section>
  <header></header>
  <div></div>
</section>

CSS

body {
  margin: 0;
}
section {
  display: flex;
  flex-direction: column;
  height: 100vh;
}
header {
  height: 150px;
  background: blue;
}
div {
  flex-grow: 1;
  background: red;
}