How to ignore/override system font size

I’m working on an app for a friend. During the development I uploaded it to ionic view and tested it.
Yesterday I invited the friend to use ionic view on his device to play around with the app before realising an official release.
Apparently my friend has modified the system font size on his device (from default to XL) and to my surprise this ruin the visibility of the app.

Bellow you can see 2 screenshots - the first is my device, and the second is from my friend device.

The most noticeable is the date picker slider, but in general the whole layout is ruined.
Is there a way to ignore or override the system font size?

Hi, can someone please explain how can I access to the font-size of the date-picker slider and set it to a specific value ?

EDIT: found it. I override ionic variable $picker-md-option-font-size.

How did you overcome the problem? I am having same issue and I cannot really find a solution for this problem. I want to fix the font size regardless of the system font size.
Thank you.