Make dropdown menu list be displayed on top of other content

Hello,

I do not know much about css and I am trying to make a recently created dropdown menu in WordPress so that it is always displayed on top of the content below it. Please see attached image for further clarification. At the moment, only the 1st entry of the menu list appears on view, while the rest get hidden behind the green section below it. I would like the dropdown menu to overlap the green section below it when opened.

I would appreciate anyone's help
Thanks
Konstantinos