JSFiddle - React, Tailwind, and code Playground

HTML

<header></header>
  <iframe src="https://freebsd.org"></iframe>
  <footer></footer>

CSS

html, body {
    height: 100%;
}

html, body, header, iframe, footer {
    margin: 0;
    padding: 0;
    width: 100%;
}

header {
    height: 34px;
    position: fixed;
    top: 0;
    left: 0;
    background-color: red;
}

iframe {
    border: none;
    height: calc(100% - 51px);
    margin-top: 34px;
}

footer {
    height: 17px;
    position: fixed;
    bottom: 0;
    left: 0;
    background-color: green;
}