CSS Z-Index

CSS z-index is a property that controls the stacking order of positioned elements on a web page, creating a three-dimensional layering effect. It determines which elements appear on top of others when they overlap, akin to arranging pieces of paper on a stack.

  • Elements exist within stacking contexts, which establish their relative position to each other.
  • The browser creates a stacking context for the root element (html) and additional contexts for elements with specific properties (position: absolute/relative/fixed, opacity < 1, transform).
  • Each positioned element within a stacking context has a z-index value, either a number (positive, negative, or 0) or the keyword auto (default).
  • Elements with higher z-index values are positioned above those with lower values.
  • Elements with the same z-index value are stacked in the order they appear in the HTML code.


div {
  position: relative; /* Establish a stacking context */
  z-index: 10; /* Place this element higher than elements with lower z-index */

Key Points:

  • z-index controls the stacking order of positioned elements (those with position other than static).
  • Higher z-index values place elements on top of lower ones.
  • position: relative or position: absolute is usually required for z-index to work.
  • Elements with the same z-index follow their order in the HTML code.
  • Nesting elements with position: relative creates stacking contexts, where z-index works within those contexts.

Common Uses:

  • Creating dropdown menus
  • Implementing modal dialogs
  • Layering images or text
  • Building interactive elements like tooltips

Mastering z-index is essential for creating visually compelling and interactive web page layouts. It empowers you to control the visual hierarchy and create engaging user experiences by carefully managing the stacking order of elements. Experiment with different values, understand stacking contexts, and craft dynamic web pages with depth and dimension!