Globally change fontsizes dynamically

I’m building an app where the font size of most elements needs to be changed on the fly (there’s a settings-section with normal/large font size).
What would be the best approach for this? (I’m new to Ionic so please provide clear instructions :wink: )
Since many components are custom, and I also override some default component font sizes, I can’t rely on $font-size-base (plus the font-size change needs to be done dynamically and ideally on the fly too…)
Any ideas?

You can create global classes applying different font sizes and switch that class using ng-class