JSFiddle - React, Tailwind, and code Playground

HTML

<div id="example">
    this is example
    <span></span>
</div>

CSS

#example{
  color:#ccc;
  font-size: 20px;
    position: relative;
    display: inline-block;
}

#example span {
    position: absolute;
    width: 100%;
    border-top: 1px solid red;
    left: 0;
    top: 0;
}