<html>
<head>
<style>
:root { --one: 10px; --another: 20px; }
</style>
<body>
<script>
document.write(getComputedStyle(document.documentElement).getPropertyValue("--one") + " " + getComputedStyle(document.documentElement).getPropertyValue("--another"))
</script>
</body>
</html.