While trying to create a new scalable way to support Dynamic Type on iOS devices, I ran into a snag where it also affected Desktop Safari font sizes. After playing around, I came up with what I believe to be new Safari and iOS CSS targeting hacks.

/* iOS browsers */
@supports(font:-apple-system-body) and (-webkit-touch-callout:default){}
 
/* Desktop Safari */
@supports(font:-apple-system-body) and (not(-webkit-touch-callout:default)){}


Hope this helps.