css z-index explained

CSS Z-Index — How Layering Works

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Ever had elements overlap in unexpected ways? Understanding how CSS Z-Index works is key to fixing layering issues on your web pages. Z-Index controls the stacking order of positioned elements on the Z-axis — what appears in front or behind. In this MiniCoursey quick guide, you’ll learn what Z-Index does, how stacking context works, and how to troubleshoot common overlapping problems in your designs.

What is Z-Index?

The Z-Index property in CSS sets the stack order of an element. An element with a higher Z-Index will appear in front of an element with a lower Z-Index, but only if it has a position other than static.

How to Use Z-Index

To use Z-Index, the element must be positioned — for example, relative, absolute, fixed, or sticky.


.box1 {
  position: absolute;
  z-index: 1;
}

.box2 {
  position: absolute;
  z-index: 2; /* appears in front of .box1 */
}

Understanding Stacking Context

Z-Index works within what’s called a stacking context. A new stacking context is created when you use certain properties like position with z-index, opacity less than 1, or transform. Elements can’t break out of their stacking context.

💡 Pro Tip: If your Z-Index isn’t working, check if your element is inside a stacking context — it might be isolated by a parent.

⚠️ Common Mistake: Setting a Z-Index without positioning won’t have any effect. Always set position first.

FAQ

Q: Can negative Z-Index values be used?
A: Yes! Negative Z-Index puts an element behind its siblings — just be careful with overlap and accessibility.

Q: Does Z-Index work on Flexbox children?
A: Yes — as long as the child is positioned, Z-Index works as expected.

Related Link

👉 Check out previous: CSS Variables vs SASS Variables — Key Differences

Where to Learn More

Use browser DevTools to inspect stacking contexts and debug Z-Index issues. MDN has great examples to practice layering complex layouts.

Conclusion

Congrats — you now know how Z-Index controls layering in CSS! Mastering this concept will help you fix overlapping issues and build neat, organized page structures.

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