Difference between auto, 0, and no z-index?

Question

What is the difference between:

1. z-index: auto
2. z-index: 0
3. no z-index at all

All the above sc

Answer 1

z-index:0 is always the "default layer" (the layer in which all elements without an explicit z-index reside), and z-index:auto means: "Sets the stack order equal to its parent". Since all the children of a parent by default start in the "z-layer 0" - relative to their parent, then, in-affect, z-index:auto and z-index:0 means the same thing: they will both be in the same "layer", and their stacking order will be according to the default stacking rules, which you can see here.