So I've been trying to develop some sort of nested drop down menu/list. I'm looking for a horizontal and also vertical nested drop down list. I am also looking to combine both horizontal and vertical elements into a list. How and where would you recommend I get a good read or information on this?

At the same time I am also trying to work on fixing up my own website's drop down menu. I keep reading you have to have the container of the menu relative and the nested things absolute or something but every time I change the things to absolute it starts cut off at the top of the page. I guess I could be reading the wrong things as recently I believe I found a few better reads but I have yet to find out how to make it simple and clean like most list I see maybe I'm just complicating my own self.

Example of my own nested list

Thanks in advance.