The z-index helps specify the stack order of positioned elements that may overlap one another. The z-index default value is zero, and can take on either a positive or negative number.
An element with a higher z-index is always stacked above than a lower index.
Z-Index can take the following values:
- Auto: Sets the stack order equal to its parents.
- Number: Orders the stack order.
- Initial: Sets this property to its default value (0).
- Inherit: Inherits this property from its parent element.
