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CSS Layout - The z-index Property

Posted: Fri Oct 27, 2023 8:23 am
by Guest
CSS Layout - The z-index Property


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

The z-index Property
When elements are positioned, they can overlap other elements.
The z-index property specifies the stack order of an element (which element should be placed in front of, or behind, the others).
An element can have a positive or negative stack order:

This is a heading

Because the image has a z-index of -1, it will be placed behind the text.


Example

img
{
 
position: absolute;
  left: 0px;
 
top: 0px;
 
z-index: -1;
}
Try it Yourself »

Note: z-index only works on positioned elements (position: absolute,
position: relative, position: fixed, or position: sticky) and flex items
(elements that are direct children of display: flex elements).







Another z-index Example

Example
Here we see that an element with greater stack order is always above an element with a lower stack order:

<html><head><style>.container {  position: relative;}
.black-box {  position: relative;  z-index: 1; 
border: 2px solid black;  height: 100px;  margin: 30px;}.gray-box { 
position: absolute;  z-index: 3;  background: lightgray;  height: 60px;  
width: 70%;  left: 50px;  top: 50px;}.green-box {  position: absolute;  z-index: 2;  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>
Try it Yourself »


Without z-index
If two positioned elements overlap each other without a z-index
specified, the element defined last in the HTML code will be shown on top.

Example
Same example as above, but here with no z-index specified:

<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>
Try it Yourself »



Test Yourself With Exercises

Exercise:
Both the header and the paragraph are positioned at the top of the page.
Make sure that the header is placed on top of the paragraph.


<style>
{
position: absolute;
top: 0;
: 1;
}
{
position: absolute;
top: 0;
: 0;
}
</style>

<body>
<h1 id="mytitle">This is a heading</h1>
<p id="myintro">This is a paragraph</p>
</body>



Submit Answer »
Start the Exercise



 CSS Property


Property
Description


z-index
Sets the stack order of an element















+1

Reference: https://www.w3schools.com/css/css_z-index.asp