Why is z-index not working?

Question

css

Guys, help.
There is img overlay on the menu (ul->li>a).
The image is superimposed on the menu, and the menu is not clickable.
Played with z-index but no result.
or am I doing something wrong?
_esthetic12.rf
(if you click on Hips or Buttocks, etc, a side menu will open)

Answer 1

position: relative
to both objects
, well, or whatever position you have there is
shorter, the position needs to be added