Adjust font size not working in HTML/JS

 Hi

I've written a simple app in HTML/CSS and JS and am uploading the files as a zip file into Mobincube.  Everything in the App works when I preview it on my phone, except the font sizes don't adjust to suit the size of the screen.  It works fine on a pc when testing different window sizes but doesn't work on various different android phones.  I first tried using vw and vh (font-size as a proportion of the viewport width or height). I then used a JS query to set the font-size to be a proportion of the screen width.

In both cases, when I open the app, the heading fills the whole screen, however if I load screen 2 and then return to screen 1 the problem seems to be fixed.  Is this a bug in Mobincube?  Any suggestions would be much appreciated.

Thank you

Simon