Navigation missing off iPad

Hello

I was given the following code to correct the navigation menu as it was missing of mobile devices:

@media handheld, only screen and (max-width: 900px) {
#show-nav-menu { display: inline-block !important; }
}

Unfortunately the code does not work for the iPad when it’s in the portrait position. In the portrait position, there is no navigation at all.

How can I fix this?

Kind regards
Oretta