<script>
internals.settings.setCSSVariablesEnabled(true);
</script>
<style>
body {
    -webkit-var-foreground: green;
    -webkit-var-background: rgb(255, 255, 255);
    color: -webkit-var(foreground);
    background-color: red;
    background-color: -webkit-var(background);
}
</style>
This text should be green on a white background. There should be no red visible.