JSFiddle - React, Tailwind, and code Playground

HTML

<div class="wrapper">
  <span class="fake-block"></span>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
  <div class="item"></div>
</div>

CSS

.item {
  width: 100px;
  height: 100px;
  background-color: black;
  float: left;
  margin: 20px;
}

.item:nth-of-type(3n) {
  background-color: red;
}

/* div.item:nth-of-type(3n+3) {
  background-color: red;
} */