JSFiddle - React, Tailwind, and code Playground

HTML

<div class="parent">
  <div class="other">Child</div>
  <div class="other">Child</div>
  <div class="mychild">Child</div>
  <div class="other">Child</div>
  <div class="other">Child</div>
  <div class="mychild">Child</div>
  <div class="other">Child</div>
  <div class="other">Child</div>
  <div class="mychild">Child</div>
</div>

CSS

.parent .mychild:first-of-type {
  text-decoration: underline;
  background: yellow;
}
.parent .mychild:nth-of-type(2){
  text-decoration: underline;
  background: red;
}
.parent .mychild:nth-of-type(3) {
  text-decoration: underline;
  background: green;
}