<!DOCTYPE html>
<html>
<head>
<script>
if (window.internals) {
    internals.invalidateFontCache();
</script>
</head>
<body>
<div style="font: 100px '.apPLesysTemUiFontMEDium';">Hello</div>
<div style="font: 100px '.AppleSystemUIFontMedium';">Hello</div>
</body>
</html>