Font size bigger as in Reader view of zo...

Hi,

I want to have a feature to give visitors the chance to resize fonts when visiting a site.
For this purpose I have tried
https://wordpress.org/plugins/zeno-font-resizer/

But so far, no much success

Any suggestion form plugins or How can I get it done?

Thanks!!

Oh ja here I have it installed:
http://kerk.h4bs.com/