button overlay issue

When using the ‘column visibility’ button on an iPhone6 and iPad, it allows the client to toggle the various columns, but doesn’t take the client back to the webpage and execute the selection. (The feature works fine on other OS').

Sample page:
http://battle-calculator.com/jurassic-world/jurassic-world-dino-creature-statistics/

Thinking it may be an overlay issue,... I've tried the following:

.dt-button-background {
z-index: 999998 !important;
}
.dt-button-collection {
z-index: 999999 !important;
}

This did not help.

Please advise, thank you in advance.