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;
}
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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>
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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>
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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