CSS Z-Index | asadmukhtar.info

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CSS `z-index`

The CSS z-index property controls the stacking order of overlapping elements. Elements with a higher z-index value appear on top of elements with a lower value.

1️⃣ How `z-index` Works

z-index applies only to elements with a position of relative, absolute, fixed, or sticky.
Elements with higher z-index values are placed in front of lower z-index elements.
Default z-index is auto (follows the document order).

2️⃣ `z-index` in Action

🔹 Example without `z-index`

.box1, .box2 {
  position: absolute;
  width: 100px;
  height: 100px;
}

.box1 {
  background: blue;
  top: 50px;
  left: 50px;
}

.box2 {
  background: red;
  top: 70px;
  left: 70px;
}

✔ Result:
Since .box2 is placed after .box1, it appears on top.

3️⃣ Using `z-index` to Control Layering

.box1 {
  position: absolute;
  background: blue;
  top: 50px;
  left: 50px;
  z-index: 2; /* Higher value, appears on top */
}

.box2 {
  position: absolute;
  background: red;
  top: 70px;
  left: 70px;
  z-index: 1; /* Lower value, appears behind */
}

✔ Result:
Now .box1 appears on top of .box2 because of the higher z-index value.

4️⃣ Negative `z-index` Values

A negative z-index places an element behind other elements.
But it can only move behind elements in the same stacking context.

.box {
  position: absolute;
  z-index: -1;
}

✔ Result:
The element moves behind other elements.

5️⃣ When `z-index` Doesn't Work

It doesn’t apply to static positioned elements.
If an element is inside a container with z-index, it follows the container’s stacking context.

To fix this, set position: relative; or another positioned value.

6️⃣ Summary Table

Property	Effect
`z-index: auto;`	Default stacking order (follows the document order).
`z-index: 1;`	Higher value, element appears in front.
`z-index: -1;`	Moves element behind others.
`z-index: 999;`	Used for popups, modals, tooltips.

7️⃣ Conclusion

The CSS z-index property helps control how elements overlap.

Use higher z-index values for elements that should be on top.
Use negative z-index values to send elements behind others.
Remember, z-index works only for positioned elements (relative, absolute, fixed, sticky).