How Does CSS Transform Affect Z-Index and Stacking Context?

How Transform Impacts Z-Index

In CSS, the transform property can have an unexpected effect on the z-index property. When applied to an element, transform establishes a new "stacking context," effectively segregating it from other elements in the rendering order.

The Issue:

You've noticed that the z-index value for your .test element seems to be ignored after applying a transform to it. This is because transform creates a stacking context, which overrides the normal z-axis stacking order.

Understanding Z-Index and Stacking Contexts:

• z-index controls the front-to-back positioning of elements within the same stacking context.
• transform creates a new stacking context, making the transformed element immune to z-index changes within that context.

Solution:

To resolve this issue and make z-index work as intended, you need to ensure that your elements are in the same stacking context. Here are two possible approaches:

1. Keep Elements in the Same Stacking Context:

Avoid applying transform directly to the element you want to position using z-index. Instead, wrap it in a container and apply the transform to the container. This will keep the child element in the parent's stacking context, allowing z-index to work effectively.

Example:

.wrapper {
  transform: rotate(10deg);
}
.test {
  z-index: -1;
}

2. Leverage Nested Stacking Contexts:

Create a series of nested stacking contexts by applying transform to multiple containers. This creates a situation where the z-index of elements within a nested stacking context is relative to each other, but not to elements outside of that context.

Remember:

When working with transform and z-index, keep the following points in mind:

• transform creates a new stacking context.
• z-index only applies within the same stacking context.
• To ensure proper z-axis positioning, keep elements within the same stacking context or use nested stacking contexts.

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