Z-index is a CSS property that controls the stacking order of overlapping HTML elements — determining which element appears visually in front of, or behind, another when they occupy the same physical space on a page.
How Z-Index Works
Elements with a higher z-index value appear in front of elements with a lower one. A popup with `z-index: 999` will display on top of regular page content sitting at the default `z-index: 0`, for instance.
Common Uses for Z-Index in Web Design
- Ensuring popups and modals display properly above all other page content
- Controlling how a sticky header or navigation bar behaves in relation to page content scrolling beneath it
- Layering decorative design elements intentionally, in a specific desired order
- Managing dropdown menus so they display correctly above surrounding content
Where This Might Come Up in WordPress
Most WordPress users never need to touch z-index directly, but it occasionally becomes relevant when customizing a theme's CSS, or troubleshooting a specific popup or menu that's stubbornly displaying behind other elements instead of properly on top of them.
A Practical Troubleshooting Tip
If a specific element is unexpectedly appearing behind another one it should logically be in front of, checking and adjusting the z-index values of both elements directly through a browser's developer tools is usually the fastest way to diagnose and properly fix the issue.
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