Help with CSS basic please

1

Hi guys.

I’m newbie in CSS

I saw a web that give css dropdown menu :

http://cssmenumaker.com/menu/grey-impression-drop-down-menu-0

but i have a question i want add a submenu inside the submenu option 1

Example:
MENU->Submenu
Submenu->Submenu
Submenu

please could you can tell me how can I do this on that menu?

thanks a lot!