IOS responsibility uk-height-viewport overlay-eff

Hello, I have purchased this tempplate and runned quickstart package. Than I have disabled everything what I did not needed (modules, articles, menus etc.)
Then I have changed top image slideshow to a single image module. Position Headerbar-a
And the only thing I have added to this site is SmartCountdown3 module and component. (position headerbar-b)
And now there is everything ok but on IOS devices. Such as iPhones and iPads. There is generated some blank space by: uk-height-viewport overlay-effect (see picture)
I have searched over all the template files to find where is setted some height of this class but nothing found.
Also the smartcountdown3 module classes etc.
Can you please advice me where to find the place where is setted the height for this class to avoid the blank space on ios devices?
address: www.double2021.cz
Thank you for any advice.

Hi there,
the viewport height is based on theme > layouts/theme.php
Headerbar A = viewport height
Headerbar B = No viewport height