Safari on iOS does some screwy stuff with numbers that are hard to override and does not respect CSS styling for certain elements in strings. I have had the same issue with dates as well. iOS recognizes elements in strings in HTML and generates the highlighting as a feature to enable the user to add a date or phone number to contacts, reminders and ical. I couldn't find a quick work around in a cursory search, but I feel pretty sure someone has created one. If the text doesn't need to be live, you could always outline the text and convert to an SVG in a graphics app. Just remember that doing so would disable screen readers.
There should be a browser class (not sure what the proper term for that is) for those elements. If you knew what the class was called you could override the built in class with custom code and style it any way you choose. You will likely need to use !important after the property to force override the built in / browser class thingy.