<!DOCTYPE html>
<html>
<head>
    <style>
        iframe {
            height: 400px;
            width: 400px;
            border: 10px solid black;
            box-sizing: border-box;
            border-radius: 50%;
        }
    </style>
</head>
<body>
    <iframe srcdoc="
	<style>
        body {
            background-color: silver;
            margin: 0;
		    transform: translateZ(0);
        }
	</style>
    "></iframe>
</body>
</html>