JSFiddle - React, Tailwind, and code Playground

HTML

<body>

<main>
  <div> </div>
  <div> </div>
</main>

</body>

CSS

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

main {
  display: flex;
  flex-direction: row;
  height: 100%;
}

@media screen and (max-width: 700px) {
    main {
        flex-direction: column;
    }
}

div {
  width: 100%;
  height: 100%;
  border: 1px solid black;
}