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

The 'z-index' property in CSS is specifically designed to manage the layering of positioned elements on a webpage. It allows developers to control the vertical stacking order of these elements, meaning that elements with a higher z-index value will be displayed above those with a lower value.

This property is only applicable to elements that have a positioning context established, such as those with 'position' set to 'relative', 'absolute', 'fixed', or 'sticky'. By utilizing 'z-index', web developers can create complex layouts where certain elements can overlap others, enhancing the overall design and user experience of the webpage.

For example, if you have a modal dialog, you would typically give it a higher z-index than the background elements to ensure it appears on top, thereby making it visually accessible to users. This is crucial in scenarios where visual hierarchy and clarity of information are important.