I made this website with an accordion menu in a sidebar on mobile, and there is one little problem i can not solve.

If you look at the page https://lieth-schule.de and open the sidebar on a mobile device (button underneath the image banner) you can see the accordion menu. If you now open a submenu, you can only scroll if you exactly hit the scrollbar of the whole sidebar.

What do I have to change in order to be able to scroll the entire sidebar, when touching and holding anywhere inside it? Like you would do on a mobile touch device?