How to make a pull down menu?

Question

css

There is an adaptive menu that is now moving out on the right,
I want to remake it so that it moves out from above by 100% height and width,
I understand that I need to place the menu above the viewport, but I didn’t get
an example from the link
https://jsfiddle.net/khorosh/0va95yxz /sixteen/

Answer 1

So?