What is the purpose of the z-index property in CSS?

The z-index property in CSS is specifically used to control the stacking order of positioned elements on a webpage. When elements overlap, the z-index allows developers to specify which element should be displayed in front of another. A higher z-index value means that the element will be positioned above those with a lower z-index value. This property is particularly important in scenarios where layering is necessary, such as dropdown menus, modals, or when creating visual effects where positioning is key.

In web design, without proper manipulation of the z-index, elements might not appear in the desired order, leading to user interface issues where important content could be obscured by other elements. Thus, knowing how to effectively use the z-index property is crucial for creating visually appealing and functionally correct web pages.