css/css-scrollbars/viewport-scrollbar.html

<!DOCTYPE html>
<meta charset="UTF-8">
<title>CSS Test: scrollbar style on root element should be propagated to the viewport</title>
<link rel="author" title="Xidorn Quan" href="https://www.upsuper.org">
<link rel="author" title="Mozilla" href="https://www.mozilla.org">
<link rel="help" href="https://drafts.csswg.org/css-scrollbars-1/#scrollbar-color-properties">
<link rel="match" href="viewport-scrollbar-ref.html">
<link rel="mismatch" href="viewport-scrollbar-mis-ref.html">
<style>
iframe {
  border: 1px solid black;
  width: 200px; height: 200px;
}
</style>
<p>Test passes if the scrollbars in the following box are styled:</p>
<iframe src="support/viewport-scrollbar-frame.html"></iframe>