Childs on Mobile not hiding when choosing another child

Hi
On mobile:
Is there any way to get the submenu children to hide, when it is not longer active?

Example. I push on one “child expander arrow”, it expands, but I want another. So I push on another, which expands too, BUT the first one does not hide. It takes a lot of space on a mobile.

I have looked at other sites of this forums users. And it is the same. So it can not be a problem at my site.

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