JSFiddle - React, Tailwind, and code Playground

HTML

<nav>
  <ul>
    <li>aaaaa</li>
    <li>bbbbbbbbb</li>
    <li>ccccccccccccccc</li>
    <li>dddddddddddddddddddddd</li>
    <li>eeee</li>
  </ul>
</nav>

CSS

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
nav {
  background: #ffc;
}

ul {
  list-style-type: none;
  
  display: -webkit-flex;
  display: flex;
  
  -webkit-flex-wrap: wrap;
  flex-wrap: wrap;
}

li {
  outline: 1px solid green;
  -webkit-flex: 1 1 20%;
  flex: 1 1 20%;
}