WebSite in mobile browser cannot access menu or download are from top

[de-jcup]

Situation

When opening https://mercedes-benz.github.io/sechub on a mobile browser (Android, Chrome) or
showing the page in a Firefox browser and reduce the visible area, the menu bar is rendered correctly,
but it is not possible to open the menue or to select the list items (red marked). The link to GitHub project page works correctly (green marked).

Wanted

As a user I want to use the menu and also to be able to use the elements from the list "Docs".