unit-rem-iframe-inside.html
<style>
:root { font-size: 20px }
body { font-size: 25px }
div { font-size: 1.5rem }
</style>
<body><div>Inside</div></body>
<style>
:root { font-size: 20px }
body { font-size: 25px }
div { font-size: 1.5rem }
</style>
<body><div>Inside</div></body>