z-index not working with fixed positioning

Question

I have a div with default positioning (i.e. position:static) and a div with a fixed position.

If I set the z-index

Answer 1

z-index only works within a particular context i.e. relative, fixed or absolute position.

z-index for a relative div has nothing to do with the z-index of an absolutely or fixed div.

EDIT This is an incomplete answer. This answer provides false information. Please review @Dansingerman's comment and example below.