JSFiddle - React, Tailwind, and code Playground

HTML

<div class="block">
  
</div>
<div class="block">
  
</div>
<div class="block">
  
</div>
<div class="block">
  
</div>
<div class="block">
  
</div>
<div class="block">
  
</div>
<div class="block">
  
</div>

CSS

.block {
  width: 300px;
  height: 100px;
  background: red;
  margin: 20px;
}
.block:nth-child(2n + 1) {
background: blue;
}