using responsive fonts and control -, control +

I am building a site using vw to make the fonts responsive but it will not work when I use control - or control + to enlarge or reduce the size of the site. Instead the font remains the same size. Using em, the font is reduced when hitting control - or + but on browsers with different displacement the font remains the same while the other features are responsive, causing problems. Is there a way around this issue to get the fonts responsive and still have control - and + to work?

Thanks,

Dan