JSFiddle - React, Tailwind, and code Playground

HTML

<form class="parent">     
    <div class="child">
      <span class="input-container">
        <input type="text" id="username" required /> 
      </span>
        <span>Username</span>
    </div>
   </form>

CSS

span.input-container:before {
  content: "|";
  border: 1px solid blue;
}