What is the default value of z-index property?

Answer 1

z-index is context-based, so even if it doesn't have a specific number value, it will always have an order in relation to other objects in the DOM.

https://css-tricks.com/css-stacking-contexts/

Answer 2

0

I think. You can alway test it.

Answer 3

Tested:
https://code.sololearn.com/Wn6B7jdl630q/?ref=app