I am going to update this and my other related posts with the answer (provided by GigaFemto - thanks) so that anyone searching for an answer in the future won't go through the long slog I did:
So,
is the required keyword.
Code:
<style type="text/css">
body { font-size: $PRINT_SCALE%; }
</style>
So,
Code:
$PRINT_SCALE