CSS Z-Index (witn Example)

Introduction

In CSS, the z-index property determines the stacking order of positioned elements along the z-axis (the axis perpendicular to the screen). It controls which elements appear in front of or behind other elements on a webpage. Here’s a concise overview:

Stacking Context: The z-index property only applies to elements with a position value of relative, absolute, or fixed. When elements overlap, the z-index value determines their stacking order within their stacking context.
Higher Values: Elements with a higher z-index value are stacked above elements with lower z-index values within the same stacking context. If two elements have the same z-index, the one that comes later in the HTML source order is displayed on top.
Negative Values: Negative z-index values are allowed and can be used to place an element behind its stacking context. Elements with negative z-index values are stacked below elements with zero or positive z-index values within the same stacking context.

img {
  position: absolute;
  left: 0px;
  top: 0px;
  z-index: -1;
}

CSS

Example

<html>
<head>
<style>
.container {
  position: relative;
}

.black-box {
  position: relative;
  border: 2px solid black;
  height: 100px;
  margin: 30px;
}

.gray-box {
  position: absolute;
  background: lightgray;
  height: 60px;
  width: 70%;
  left: 50px;
  top: 50px;
}

.green-box {
  position: absolute;
  background: lightgreen;
  width: 35%;
  left: 270px;
  top: -15px;
  height: 100px;
}
</style>
</head>
<body>

<div class="container">
  <div class="black-box">Black box</div>
  <div class="gray-box">Gray box</div>
  <div class="green-box">Green box</div>
</div>

</body>
</html>

CSS

Output

Conclusion

In conclusion, z-index is a crucial CSS property for controlling the stacking order of elements on a webpage. By assigning different z-index values to positioned elements, developers can control their visual hierarchy and ensure elements appear in the desired order on the z-axis. Understanding how z-index works and its interaction with stacking contexts is essential for creating complex layouts and resolving stacking order issues in web development projects. While z-index provides powerful control over element stacking, it’s important to use it judiciously and with careful consideration to avoid unintended consequences and maintain a clear and intuitive visual hierarchy in the user interface.

Frequently Asked Questions

Q1. How does z-index work in CSS?

z-index is a CSS property that controls the stacking order of elements along the z-axis. Elements with higher z-index values are stacked above elements with lower values within the same stacking context.

Q2. Can I use z-index with all HTML elements?

No, z-index only applies to elements with a position value of relative, absolute, or fixed. These elements create a stacking context and z-index determine their stacking order within that context.

Q3. What happens if two elements have the same z-index value?

If two elements have the same z-index value, the one that comes later in the HTML source order will be displayed on top.

Q4. Can I use negative z-index values?

Yes, negative z-index values are allowed. They can be used to place an element behind its stacking context or other elements with zero or positive z-index values within the same stacking context.

Q5. How do I debug z-index issues in my layout?

To debug z-index issues, you can inspect elements using developer tools in your browser. Check the z-index values of the elements involved and ensure they’re positioned correctly within their stacking contexts. Adjust z-index values as needed to achieve the desired stacking order.