iOS Cordova

For one of my legacy games, which has been published on Android (using Cordova), Chrome Web Store, Facebook Web and [login to view URL] I'm trying to push this to Messenger (Facebook Instant Games) and on iOS using Cordova. Surprisingly, the game works fine on Facebook Instant Games, but only on Android, on iOS I can see only background of the game. It seems to me if it'll work on Facebook Instant Games iOS it'd also work on Cordova iOS. The game is based on HTML5 Canvas API, initially I was thinking that's happening because of using Web Workers. However, debugging showed that's not the case, there's a simply one problem with... CSS. Somehow the iOS browser reads it in a different way, which I can't figure out. In the attachment you can find code, which is ready-to-launch using Xcode on your iOS device. In the code you can also find 1 TODO in [login to view URL] at line 76. When you'll comment out "display: none" then the game on iOS will show all the elements, but then there's still some work to be done on JS/z-index side, which once again - I can't figure out. Just in case, for some basic button I've tried to set up an alert and the touch gesture is working as expected. Anyways, the game has been published on Android more than 2 years ago and works perfectly fine. Final screenshots/video from iOS device is required, therefore you MUST have iOS device with Xcode. Please check "Files"/"Attachments" to see the codebase, and please don't send me an automatic bids without taking a look into the code.