The issue arises because of the z-index applied to the parent element, causing the child element to stack relative to other elements within the same parent.
When you specify a z-index value for an element (other than auto), that element creates its own stacking context. This results in all descendants of the element having their own stacking order in relation to the ancestor element.
For example, if the parent has a z-index of 9 and the child has a z-index of 8, it's as if you are giving them a z-index of 9, 8 respectively.
You can refer to this article for a more detailed explanation.
To resolve this, try removing the z-index from the parent element and setting the sibling element to z-index: -1. This workaround may vary in different browsers, but it should work in Chrome at least.
Take a look at the updated fiddle for reference.
I hope this solution helps you out.