What is the purpose of the z-index and how is it used?

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.