JSFiddle - React, Tailwind, and code Playground

HTML

<header>
  <ul>
    <li>Log In</li>
    <li>Sign Up</li>
  </ul>
</header>

CSS

* {
  box-sizing: border-box;
}
body {
  margin: 0;
  padding: 0;
}
header {
  width: 100%;
  background-color: #00A0F0;
  margin: 0;
  padding: 15px;
  float: left;
}
ul {
  width: 100%;
}
ul li {
  display: inline-block;
  float: left;
  color: #fff;
  list-style-type: none;
  padding: 5px 10px;
  position: relative;
}
ul li:not(:last-child)::after {
  content: '';
  width: 1px;
  height: 100%;
  display: block;
  background-color: #fff;
  position: absolute;
  top: 0;
  right: 0;
  opacity: 0.6;
}