Understanding the Z-Index Property in HTML

Understanding the Z-Index Property in HTML


4 min read

The z-index property can be specified with an integer value (positive, zero, or negative), which represents the position of the element along an imaginary z-axis. If you are not familiar with the term 'z-axis', imagine the page as a stack of layers, each one having a number. When working with HTML and CSS, one of the most important concepts to grasp is the z-index property.

The z-index property is used to determine the order in which elements are stacked on a webpage. It assigns a numerical value to an element, defining its position relative to other elements. Elements with higher z-index values will appear on top of those with lower values.

By default, elements have a z-index of 0, but this can be changed to positive or negative numbers, including decimals. Despite its power, it can sometimes create unexpected behaviors in your layout. In this blog post, we will delve into the causes of these issues and explore some common solutions.

Example on Codepen

Possible Causes of Z-Index Issues

  1. Insufficient z-index Values

    The stacking order of elements can be disrupted when z-index values are not properly assigned. For instance, if multiple elements are assigned the same z-index value or if some elements have no z-index value specified, conflicts may arise.

  2. Inherited z-index:
    Elements within nested structures may inherit the z-index values from their parent elements, causing unexpected stacking behavior. This can be problematic when dealing with complex layouts, such as dropdown menus or modals. Make sure to pay attention to each element's z-index and avoid relying solely on parent containers

  3. Context and Positioning

    The positioning of elements can affect their stacking order. Elements with relative, static, or fixed positioning can stack differently. Without proper positioning, the z-index property may not have any effect.

  4. Overlapping z-index values

    Assigning the same z-index values to multiple elements can create complications. If elements are overlapping and have the same z-index, their stacking order is determined by the order they appear in the HTML markup.

Solutions to Z-Index Issues:

  1. Assign Proper Z-Index Values

    To avoid conflicts, ensure that each element has a unique z-index value assigned. By organizing elements into logical groups, you can create a clear hierarchy and prevent overlapping issues.

  2. Adjust Positioning

    Experiment with different positioning values, such as relative, absolute, or fixed positioning, to determine the optimal stacking order for your elements. Keep in mind that elements with higher stacking orders should be positioned later in the HTML markup.

  3. Use CSS3 Stacking Context

    CSS3 introduces a concept of stacking contexts, which can help separate and organize elements into distinct layers. By creating stacking contexts, you can control the stacking order within specific sections of your layout.

  4. Modify Parent Stacking

    Be mindful of how parent elements may affect the stacking of child elements. Explicitly set the z-index of parent elements and use position: relative or position: absolute when necessary to prevent unwanted inheritance.

  5. Isolation property

    In CSS, the isolation property allows you to isolate certain elements and create a stacking context for them. When an element has isolation set to "isolate," it creates a new stacking context for its children, separating them from the rest of the document. This means that z-index values of isolated elements only affect their children, keeping them contained within their stacking context. Isolation is useful when you want to prevent elements within a specific container from being affected by the z-index values of elements outside that container.

     .isolation {  
       isolation: isolate;

    For example, imagine you have a dropdown menu that needs to appear above other elements on your webpage, regardless of their z-index values. By isolating the dropdown container, you can ensure that its z-index values don't interfere with the stacking order of other elements. To implement isolation, you need to set the isolation property to "isolate" on the parent element. The isolated element creates its stacking context, and any z-index values assigned to its children won't affect elements outside of that context.


The z-index property allows you to control the stacking order of elements, while the isolation property enables the creation of separate stacking contexts. Understanding the z-index property and how it affects the stacking order of elements is crucial for web developers. By diagnosing the potential causes of z-index issues, such as incorrect or inherited z-index values, and applying the appropriate solutions.
Thanks, Happy coding!!!