Z-Index

Understanding Z-Index

Z-index is a CSS property that determines the stacking order of elements on a webpage. Higher z-index values indicate that elements appear closer to the user, obscuring elements with lower values.

Key Concepts

• Z-index: auto: Inherits the z-index value from the parent element.
• Z-index: 0: Positions the element in the normal flow of the document, with no stacking effect.
• Z-index: 1: Positions the element above its siblings (within the same parent) in the normal flow.
• Z-index: Positive values: Stacks the element above its siblings, with higher values appearing closer to the user.
• Z-index: Negative values: Positions the element below its siblings, with lower values appearing further away.

CSS Example: Stacking Elements

.layer1 {
  position: absolute;
  z-index: 1;
  background-color: red;
}

.layer2 {
  position: absolute;
  z-index: 2;
  background-color: blue;
}

Explanation:

• The position: absolute property positions elements absolutely within their parent container.
• The z-index property assigns a stacking order to the elements:
  • layer1 has a z-index of 1, so it will appear above the normal flow of the document.
  • layer2 has a higher z-index of 2, so it will stack above layer1 and be visible on the webpage.

Accessibility and Ease of Use

Z-index can impact accessibility by ensuring that important elements are visible to users. For example, a modal dialog should have a high z-index to prevent users from interacting with other page elements behind it.

Tips for Clear and Concise Use

• Use z-index sparingly to avoid unnecessary stacking.
• Set the z-index values explicitly to avoid unexpected behavior.
• Test your designs across different browsers and devices to ensure consistent stacking.