JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
<nav>
  Navigation
</nav>

<main>
  <div class="sc">
    This should be square
  </div>
</main>
</div>

CSS

html, body {
      margin: 0;
      height: 100%;
      background-color: #fff;
    }
    .wrapper {
      display: flex;
      align-items: center;
      height: 100%;
    }
    nav {
      float: left;
      height: 100%;
      width: 96px;
      background-color: #666;
    }
    main {
      float: left;
      width: calc(100% - 96px);
      height: 100vmin;
      max-height: calc(100vw - 96px);
    }
    .sc {
      margin: 0 auto;
      background-color: #000;
      color: #fff;
      height: 100vmin;
      width: 100vmin;
      max-width: 100%;
      max-height: calc(100vw - 96px);
    }