CSS z-index

Subject: css

CSS z-index

The z-index property in CSS controls the stacking order of elements along the z-axis (front-to-back). It only works on elements that have a positioning context (relative, absolute, fixed, or sticky).

Higher z-index values appear in front of lower values.

Syntax

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  • The number can be positive, negative, or zero.
  • The default value is auto.

Use Cases

  • Creating overlapping components (e.g., modals, sidebars)
  • Ensuring dropdowns appear above content
  • Controlling visibility layers in interactive interfaces

Example: CSS z-index in Action

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Important Notes

  • z-index only works on positioned elements (relative, absolute, fixed, sticky)
  • Higher z-index values are displayed on top
  • If two elements have the same z-index, the one that appears later in the HTML wins
  • Negative values can push elements behind others (even behind the page)

Common Mistake: Non-positioned Elements

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Key Takeaways

  • z-index sets the stacking order of overlapping elements
  • Requires a non-static position property to work
  • Higher values bring the element closer to the user (in front)
  • Ideal for managing dropdowns, tooltips, modals, and layered UIs
  • Always combine with correct positioning for consistent behavior
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