Z Index in CSS

#css #beginners #webdev #styling

Hey Guys, I am Garvit Motwani. In This article i will tell you about the z-index property in CSS.

What is a Z Index?

The z-index property specifies the stack order of an element.

An element with greater stack order is always in front of an element with a lower stack order.

The z-index property is specified as either the keyword auto or an <integer>.

Note: z-index only works on positioned elements (position:absolute, position:relative, or position:fixed).

What does the values do?

auto
The box does not establish a new local stacking context. The stack level of the generated box in the current stacking context is the same as its parent's box.

<integer>
This <integer> is the stack level of the generated box in the current stacking context. The box also establishes a local stacking context in which its stack level is 0. This means that the z-indexes of descendants are not compared to the z-indexes of elements outside this element.

Syntax And Values

/* Keyword value */
z-index: auto;

/* <integer> values */
z-index: 0;
z-index: 2;
z-index: 300;
z-index: -1; /* Negative values to lower the priority */

/* Global values */
z-index: inherit;
z-index: initial;
z-index: unset;

Example

HTML

<h1>The z-index Property</h1>

<img src="cat.jpg" width="100" height="140">

<p>Because the image has a z-index of -1, it will be placed behind the heading.</p>

CSS

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

This will look like this:

HTML

<div class="dashed-box">Dashed box
  <span class="gold-box">Gold box</span>
  <span class="green-box">Green box</span>
</div>

CSS

.dashed-box { 
  position: relative;
  z-index: 1;
  border: dashed;
  height: 8em;
  margin-bottom: 1em;
  margin-top: 2em;
}
.green-box { 
  position: absolute;
  z-index: 3; /* put .green-box above .green-box and .dashed-box */
  background: green;
  width: 80%;
  left: 60px;
  top: 3em;
}
.blue-box { 
  position: absolute;
  z-index: 2; /* put .blue-box above .dashed-box */
  background: blue;
  width: 20%;
  left: 65%;
  top: -25px;
  height: 7em;
  opacity: 0.9;
}