JSFiddle - React, Tailwind, and code Playground

HTML

<div style="height:321px">
    <div class="frame">
      <iframe id="myframe" width="100%"></iframe>
    </div>
</div>

CSS

.frame {
    height: 100%;
}

JavaScript

with (document.getElementById ('myframe')) {
 setAttribute('height', parentElement.clientHeight);
 contentDocument.body.innerHTML = 'My height is ' + clientHeight + 'px';
}