Z-Index

You might say

This dialog is getting covered by other content. Make sure it stays on top.

Control which overlapping layer appears on topZ-index affects the stacking order of positioned elements inside a stacking context. A larger number does not always escape its parent. Define a short layer scale for content, sticky UI, menus, overlays, and dialogs instead of solving each overlap with a larger random number.

Know first

Position

z: 1 z: 2 z: 3

You can say this to an AI Agent

The dropdown is clipped despite a large z-index. Inspect parent overflow, positioning, and stacking contexts before changing the layer strategy; do not keep increasing numbers. Verify it clears the card without covering modals or global navigation.

When to use it

Keep a dropdown above nearby content
Delete this project?
CancelDelete
Place a dialog above its backdrop
Navigation · z-index: 100
Order sticky and floating elements
All statesAll statesIn progress
Create a shared layer scale
Content 1Sticky header 100Overlay 1000Dialog 10000

When NOT to use it

Keep increasing the number without checking the stacking context
z-index: 99, but no position is set
Give every component its own arbitrary z-index
z-index: 9999z-index: 99999z-index: 999999
Place ordinary content above a modal
Parent z-index: 1Child 9999z-index: 2
Use layering to hide a layout or clipping problem
Content that appears earlier in the codeUse z-index to force a different stacking orderIf the visual order should match the document order, adjust the DOM structure first.

Anatomy

z-index: 1z-index: 2The big one is on top

The z-index is small and is suppressed below.

The z-index is larger and covers it.

The stacking value used to position elements and flex/grid items; it also depends on the stacking context in which it is located.

Variants

1 ~ 10

The card corner mark and avatar are slightly overlaid.

100

Fixed bar suppresses scrolling content

1000

Page1000

Drop-down, bubble, text prompt

10000

Example gear: Make the modal layer higher than the ordinary page floating layer

Typical use cases

Dropdown layer

Page z-index: 1

Mask z-index: 1000

Pop-up z-index: 1001 Confirm to log out?

Sticky header

Document Center Guidelines API z-index: 100

In the same cascading rule, the navigation level is higher than the scrolling content

Modal

Task list In progress ▾

z-index: 1000

All

In progress ✓

Completed

The drop-down floats on top of the card and is neither covered nor cut

Tooltip

＋ z-index: 10

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A dropdown already has z-index: 99999 but is still clipped at the card boundary. What should be inspected next?

A. Keep increasing the dropdown's z-index to a larger numberB. Inspect parent overflow, positioning, and stacking contextsC. Increase the z-index of the card and every child together