JSFiddle - React, Tailwind, and code Playground

HTML

<nav>
  <i></i>
  <i></i>
  <i></i>
</nav>
<main></main>

CSS

/* Code to Troubleshoot
// ----------------- */

body {
  display: -webkit-flex;
  display: flex;
}

nav {
  -webkit-flex-basis: 160px;
          flex-basis: 160px;
  z-index: 2;
}

main {
  -webkit-flex: 1;
          flex: 1;
  position: relative;
  min-width: 1px;
  max-width: 400px;
  margin: 0 auto;
  z-index: 1;
}


/* Presentational Styles
// ------------------ */

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  padding: 0;
  font-family: sans-serif;
  font-weight: 300;
  color: #bbb;
  background-color: #eaeaea;
}

nav,
main {
  height: 100vh;
  background-color: #fff;
  box-shadow: 0 0.15em 0.65em rgba(0, 0, 0, 0.15);
}

nav {
  counter-reset: linkCount;
}

nav i {
  display: block;
  border-bottom: 1px solid #eaeaea;
  padding: 0.925em 1em;
  font-style: normal;
  line-height: 1;
}

nav i:before {
  counter-increment: linkCount;
  content: "Link " counter(linkCount);
}

main:before {
  content: "Main Content";
  display: block;
  position: absolute;
  top: 50%;
  left: 50%;
  text-align: center;
  -webkit-transform: translate3d(-50%, -50%, 0);
          transform: translate3d(-50%, -50%, 0);
}