Loading lesson path
Concept visual
Formula
The z - index property specifies the stack order of positioned elements.The stack order defines which element should be placed in front or behind other elements. When elements are positioned, they can overlap other elements.
Formula
An element can have a positive or negative stack order (z - index):Formula
Because the image has a z - index of - 1, it will be placed behind the text.{
position: absolute;
left: 0px;
top: 0px;
z-index: -1;
}Formula
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).
A positioned element with a 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">
Formula
< div class ="black - box"> Black box </div >
< div class ="gray - box"> Gray box </div >
< div class ="green - box"> Green box </div ></div> </body> </html>
If several positioned elements overlap each other without a z-index specified, the elements render in the order they are defined in the HTML source code.
Formula
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">
Formula
< div class ="black - box"> Black box </div >
< div class ="gray - box"> Gray box </div >
< div class ="green - box"> Green box </div ></div> </body> </html>