Product photo popup aspect ratio on mobiles

-- url of the page with the problem -- : lambcuts.net
-- HikaShop version -- : 3.2.1
-- Joomla version -- : 3.8.1
-- Error-message(debug-mod must be tuned on) -- : none

Hello,

When I click on a product thumbnail using a mobile device, the enlarged popup photo loses its original aspect ratio so that the width is reduced to fit the width of the device screen but the height remains the same.

Is this an issue with hikashop or my template? If it's with hikashop, how do I correct this?

Thanks,
Hein