JSFiddle - React, Tailwind, and code Playground

HTML

<ul class="list-item">
  <li>list item 1</li>
  <li>list item 2</li>
  <li>list item 3</li>
  <li>list item 4</li>
  <li>list item 5</li>
  <li>list item 6</li>
  <li>list item 7</li>
  <li>list item 8</li>
  <li>list item 9</li>
</ul>

CSS

.list-item li {
  width:30%;
  display:inline-block;
  margin-bottom: 2px;
  color: #fff;
  padding: 1px;
 }
.list-item li:nth-child(3n+0) {
  background: red;
}
.list-item li:nth-child(3n+1) {
  background: green;
}
.list-item li:nth-child(3n+2) {
  background: blue;
}