JSFiddle - React, Tailwind, and code Playground

HTML

<div class="menu">

</div>
<div id="container">
  <iframe scrolling="no" onload="resizeIframe(this)"...

CSS

#container { width: 100%; height: 100%; }
iframe { width: 100%; height: 100%; border: 0; }
html,body { margin: 0; height: 100%; }
.menu { height: 30px; background: red; }

JavaScript

function resizeIframe(obj) {
    obj.style.height = obj.contentWindow.document.body.scrollHeight + 'px';
}