Why does z-index not work?

html

responsive-design

positioning

css-jenga

byAnton Shumikhin·Nov 24, 2024

For z-index to function correctly, an element must have a position property set to relative, absolute, fixed, or sticky. The static position, however, doesn't allow z-index to work effectively. The application of z-index is limited to elements within the same stacking context. In layman's terms, a parent with a z-index of 1 cannot impact a child with a z-index of 2 in a different context.

/* CSS */
.positioned {
  position: relative;
  z-index: 42; /* Meaning of life and depth in layout positioning! */
}

<!-- HTML -->
<div class="positioned">I'm the king of CSS world!</div> <!-- Layered above others -->

Unraveling the concept of stacking context

Stacking contexts, sometimes misunderstood, are vital to mastering the z-index. A plethora of properties like opacity, flexibility, and transforms can create new stacking contexts, not just z-index alone. Note well that elements within nested or child stacking contexts are limited to their parent context. Regardless of how high the child's z-index, the parent's z-index confines it.

Position: sticky - not always your best friend

Using position: sticky comes with its foibles. Beware of its inconsistent browser compatibility, especially with legacy browsers or specific mobile environments. It also behaves distinctly from absolute or fixed, focusing on the nearest scrolling ancestor and containing block, as opposed to the viewport.

Tackling complex scenarios

Let's navigate through some more complex, real-world scenarios.

Nested z-indexing: Ensure you understand the hierarchy and their respective stacking contexts, especially when nested elements have conflicting z-index values.
Flex and Grid containers: In a CSS3 context, flex and grid items can use z-index without explicitly set positioning, leading to potentially surprising outcomes.
Negative z-index values: Using negative z-index values can result in objects being hidden beneath the backdrop or disappearing from the screen — it's like being sentenced to the CSS phantom zone!
Effective stacking with relative positioning: Relative positioning simplifies the management of complex layouts by assigning a clear stacking context.

When `position: absolute` isn't enough

Going absolute with positioning isn't the ultimate fix. It removes the element out of the document’s natural layout flow. Plus, if a parent element with relative positioning enfolds an element with absolute positioning, the child gets limited within the boundaries of the parent's stacking context, thwarting its rendezvous with the top position.

Debugging tips and tricks

Unravel z-index mysteries with a concise debugging process:

Examine element's lineage: Browser developer tools can help trace an element's hereditary line.
Clarify position properties: Check if elements have a non-static position.
Dissect stacking contexts: Discern which elements form their context and plan your layout accordingly.
Tweak z-index values: Increment or decrement z-index values to test their effect on stacking. It's like playing CSS Jenga!