I don't see any different by using z-axies .

Question

its same like the previous one

Answer 1

You tag 'z-index" and you say 'z-axis'... what do you expect as result?

It seems like if you make a mistake, if you think to see 3d effect with 'z-index': this property control order of displaying positionned elements ( work only on element with a property 'position' set ) when they overlap each others... higher values elements masking lower...

Otherwise, you can apply 2d and 3d effects with css... but like 'z-index' apply only on particular wrapper, these transforms require also a particular container context. For more informations, look at 'transform' css property:
https://developer.mozilla.org/en-US/docs/Web/CSS/transform

Answer 2

maybe that's because none of the elements on your page overlay another one.