<!DOCTYPE html>
<html>
<head>
<title>Hidden overflow on HTML, hidden overflow on BODY</title>
</head>
<body style="background:white; color:black;">
<div style="overflow-y:auto; overflow-x:hidden; width:20em; height:20em; background:cyan;">
<p>This text should be inside a vertically scrollable cyan box.</p>
<p>The viewport should not have scrollbars.</p>
<div style="width:300vw; height:300vh;"></div>
</div>
</body>
</html>