JSFiddle - React, Tailwind, and code Playground

HTML

<h2>
Something
</h2>

CSS

h2 {
  position: relative;
  z-index: 1;
  text-align: center;
  padding-bottom: 50px;
}

h2:after {
  content: "";
  position: absolute;
  left: 50%;
  bottom: 0;
  width: 100px;
  border-bottom: 2px solid magenta;
}