What is the issue with z-index when using positioned tags?

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When using positioned elements in HTML and CSS, the z-index property specifies the stack order of an element. However, if the z-index values of elements are not set correctly or conflicting, it can lead to unexpected and unintended layering of elements on top of each other, resulting in parts of the page appearing hidden or lost. It can be difficult to debug and fix z-index issues, especially in complex layouts with many nested elements.