Drop down navigation bar

Hello everyone.
My question is about the drop down navigation bar.
its appears on my website in a responsive mode,but i can’t open it.

then,if i add this css additional
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.main-navigation .mainnav-mobi ul {
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display: inline;
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}

In this case it works but it’s always open,once i open a new page.

So i’d like to have a navigation bar and open it only if i tap on it.

Thanks in advance for your support and help

The page I need help with: [log in to see the link]