Dynamic set font size conundrum


I’m currently using ionic to build a windows store app to be primarily used on tablets and have done pretty well making ionic play nice and suit the needs so far.

However I’d like to allow a user to increase/decrease font sizes across the app as a setting option. The problem though, is everything in ionic appears to be hardset PX for font’s instead of rem,em. I’m kind of stumped how to make that possible, could anyone maybe point me in a direction I’m not apparently thinking of that might allow me to do so?

Normally I could just change the setting at the document level if everything else was set in rem etc for fonts, except without that available, I’m at a roadblock at the moment as to how to accomplish dynamic font size changes app-wide?