How Do CSS Transforms Affect Z-Index and Stacking Order?

Z-Index and Transform: A Detailed Explanation

When using CSS transformations, it's important to understand their interaction with z-index. In some cases, applying a transform can cancel out the intended z-index behavior.

Understanding Stacking Contexts

Z-index and transform both establish their own "stacking contexts." Essentially, a stacking context creates a new stacking order for elements. One key rule is that z-index only affects the order of elements within the same stacking context.

Z-Index and Transform Interactions

In the example code, the .test element has a transform property set, which creates its own stacking context separate from the default context established by the HTML element.

The pseudo-element .test:after is positioned within the stacking context of .test. However, setting its z-index: -1 does not place it behind .test, as z-index applies only within its own context.

Resolving the Z-Index Issue

To ensure correct z-index behavior, make sure that related elements share the same stacking context. In this case, you want to rotate .test while still preserving the shared stacking context.

Solution: Using a Container

By placing .test inside a container element, such as .wrapper, and applying the transform to .wrapper instead, you can still achieve the desired rotation while maintaining the stacking context between .test and its child elements.

Conclusion

Transformations do not directly cancel z-index, but they can create separate stacking contexts. Understanding this interaction allows you to make the necessary adjustments and ensure that z-index functions as intended in complex layout scenarios.

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