JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
  <li><a href="">List item 1</a></li>
  <li><a href="">List item 2</a></li>
  <li><a href="">List item 3</a></li>
  <li><a href="">List item 4</a></li>
  <li><a href="">List item 5</a></li>
  <li><a href="">List item 6</a></li>
  <li><a href="">List item 7</a></li>
  <li><a href="">List item 8</a></li>
  <li><a href="">List item 9</a></li>
</ul>

CSS

ul {
  position: relative;
  list-style: none;
  margin: 0;
  padding: 0;
  -moz-column-count: 4;
  -webkit-column-count: 4;
  column-count: 4;
  }

li:last-child:before {
  position: absolute;
  content: " ";
  display: block;
  background-color: red;
  height: 1px;
  top: -1px;
  width: 100%;
  left:0;
  }