JSFiddle - React, Tailwind, and code Playground

HTML

<html>
<body>
  <header>header</header>
  <div id="content">
    <nav>nav</nav>
    <iframe src="https://fiddle.jshell.net"></iframe>
  </div>
</body>
</html>

CSS

body, html {
  height:100%;
  margin:0;
  padding:0;
}

body {
  display:flex;
  flex-direction:column;
}

header {
  background:red;
  height:40px;
  width:100%;
}

nav {
  background:green;
  width:100px;
}

#content {
  display:flex;
  height:100%;
}

iframe {
  flex:1;
  background:grey;
  border:none;
}