JSFiddle - React, Tailwind, and code Playground

HTML

<body>
  <div class="content">
    Hello World!
  </div>
  <div class="spacer"></div>
  <footer class="footer"></footer>
</body>

CSS

body {
  margin: 0;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

.spacer {
  flex: 1;
}

.footer {
  height: 50px;
  background-color: red;
}