JSFiddle - React, Tailwind, and code Playground

HTML

<div class="flex-child green">
    <p id="a">You clicked on: </p>
    <iframe
      id="zzz"
      srcdoc="<html><h1>hello</h1><button>click me!</button></html>"
      width="500"
      height="500"
    ></iframe>
  </div>

CSS

.flex-container {
    display: flex;
  }

  .flex-child.green {
    flex: 1;
  }

JavaScript

document.getElementById("zzz").addEventListener('load', iframeLoaded)

 function iframeLoaded() {
   document.getElementById("zzz").contentWindow.addEventListener('click', function(e) {
     document.getElementById("a").innerHTML = e.target.tagName;
   })
 }