Introduction to Opacity in CSS
You name a feature or property, and the cascading style sheet has it. It is full of options which keep expanding as you explore more. Many a time, we come across an image, which appears opaque or transparent. Sometimes, hovering over an object changes its opacity too. All this is handled by the CSS property, Opacity. A developer can select how opaque an element must look on their page, by making the use of this property. This feature is majorly used in over-lay screens such that the content of the main page is visible as well as that of the overlay screen.
Syntax
The syntax for opacity is:
opacity:value (percentage/decimal)
This property can be used in styling any element. Just like other features, it can be added along. The developers can add the opacity, as and when required.
Examples to Implement Opacity in CSS
Let us take a look at some of the examples to understand better.
Example #1
Demonstration of opacity using external CSS and hover feature
For this example, we are using external CSS. Hence we will start off by creating the CSS file first. In the CSS file, we will write the styling for paragraph element. To demonstrate the opacity feature, we will write a hover sub-class, where the opacity feature will be used.
CSS coding should be as follows:
Code:
p{
background-color: blueviolet;
color: white;
font-family: Cambria, Cochin, Georgia, Times, 'Times New Roman', serif;
height: 150px;
width: 150px;
font-style: bold;
}
p:hover{
opacity: 50%;
}
- Now, the HTML code for this example will be very basic. Firstly, in the head section, we will call the external style sheet.
- Then, in the body section, we will use the paragraph element <p> such that the opacity feature can be demonstrated. The code for the HTML file will be as follows:
<html>
<head>
<title>Opacity Demo</title>
<link rel = "stylesheet" href = "opacity.css">
</head>
<body>
<h2>Opacity Demo</h2>
<p>Hovering over this box, will make it opaque. Try it.</p>
</body>
</html>
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- Once we will save this file and open it through a browser we will see the following output:
- Hovering over the box will make it opaque like this:
Example #2
Use of opacity in overlay screen through external CSS
For this example, we will use external CSS. Hence we will start by creating the CSS. In the CSS file, we will first create an ID that will have the styling for the overlay screen.
The code for the same will look like this:
Code:
#ID1{
position: fixed;
display: none;
height: 50%;
width: 50%;
background-color: lightblue;
opacity: 50%;
cursor: pointer;
}
- We will also define a class, which will have the styling property of the content on the overlay screen. The code will look like this:
.content{
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
color: darkblue;
margin: 100px;
}
- Combining the ID and the class, the final CSS class will look like this:
#ID1{
position: fixed;
display: none;
height: 50%;
width: 50%;
background-color: lightblue;
opacity: 50%;
cursor: pointer;
}
.content{
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
color: darkblue;
margin: 100px;
}
- Next, we will code for the HTML page. Since this example uses external CSS, we will call the external CSS file in the head section.
- Now, since we need the overlay screen, we will define some JavaScript functions. This will be coded in the body section within the script tag. The code for the same will look like this:
<script>
function up() {
document.getElementById("ID1").style.display = "block";
}
function down() {
document.getElementById("ID1").style.display = "none";
}
</script>
- Now, using these functions and CSS script, we will code for the <div> element in the body section, as follows:
<div id="ID1" onclick="down()">
<div class="content">OVERLAY SCREEN TEXT</div>
</div>
<h2>CLICK TO SEE EFFECT OF OPACITY IN OVERLAY SCREEN</h2>
<button onclick="up()">Overlay effect UP</button>
- Hence, the final HTML code should look like this:
<html>
<head>
<title>Overlay Demo</title>
<link rel = "stylesheet" href = "overlay.css">
</head>
<body>
<script>
function up() {
document.getElementById("ID1").style.display = "block";
}
function down() {
document.getElementById("ID1").style.display = "none";
}
</script>
<div id="ID1" onclick="down()">
<div class="content">OVERLAY SCREEN TEXT</div>
</div>
<h2>CLICK TO SEE EFFECT OF OPACITY IN OVERLAY SCREEN</h2>
<button onclick="up()">Overlay effect UP</button>
</body>
</html>
- Saving this file and opening it through a browser will give this output:
- Clicking on the button will make the overlay screen pop-up and give this output:
Clicking anywhere on the overlay screen will make it vanish.
Example #3
Opacity using internal CSS
Since we are using internal CSS, we will directly code for the HTML page. In the head section, we will define the style with the <style> tag.
The code should be as follows:
Code:
<style>
p{
background-color: green;
color: white;
font-family: Cambria, Cochin, Georgia, Times, 'Times New Roman', serif;
height: 150px;
width: 150px;
font-style: bold;
}
p:hover{
opacity: 50%;
}
</style>
- Now, in the body section, we will call paragraph element <p> such that the opacity feature can be demonstrated.
- The final HTML code should look like this:
<html>
<head>
<title>Opacity Demo</title>
<style>
p{
background-color: green;
color: white;
font-family: Cambria, Cochin, Georgia, Times, 'Times New Roman', serif;
height: 150px;
width: 150px;
font-style: bold;
}
p:hover{
opacity: 50%;
}
</style>
</head>
<body>
<h2>Demo of Opacity</h2>
<p>Hovering over this box will make it opaque!</p>
</body>
</html>
- The output of the html page will look like this if opened through a browser:
- Hovering over the green box will make it opaque like below screenshot:
Explanation: In the above example we saw various ways and purposes which make use of the opacity property. However, it is not just limited to the above options. One can try experimenting with images and set the desired opacity. This is a feature that can be used depending on the user requirement. Using such features efficiently will add on to better end-user experience. Developers are free to check and play around with various CSS features in different combinations to obtain various results accordingly.
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This is a guide to Opacity in CSS. Here we discuss an introduction to Opacity in CSS with syntax, and examples to understand the use of opacity in a better way. You can also go through our other related articles to learn more –
