How to Use the CSS Opacity Property

See CSS: Tips and Tricks for similar articles.

CSS3's opacity property makes it easy to change the opacity of images, text, <div>s, and other elements. Where before we might have resorted to images with a semitransparent alpha setting, we can now change the opacity via CSS. Even better, we can change opacity more easily with :hover to create rollover effects. Let's look at an example:

Start with the following HTML page:


<!DOCTYPE html>
<html>
<head>
	<meta charset="utf-8">
	<title>CSS3 Opacity</title>
	<style type="text/css">
		#caption {
			background: #fff;
			width:300px;
			position:relative;
			top:-100px;
			opacity: .5;
		}
		#caption:hover {
		}
	</style>
</head>
<body>
<div id="main">
	<h1>CSS3 Opacity</h1>
	<img src="Images/chicago.jpg" alt="Chicago skyline" id="img1">
	<div id="caption">The Willis Tower (formerly known as the Sears Tower) is 1450 feet tall.</div>
</div>
</body>
</html>

The opacity property modifies the percent opacity of the element it's applied to. A setting of 0 means that the element should be invisible, and a setting of 1 means that it should be 100% opaque. To make the caption on the picture in our page semi-transparent, change its opacity to .5.
```
#caption {
	background: #fff;
	width:300px;
	position:relative;
	top:-100px;
	opacity: .5
}
```
The result will look like this:
To make the caption opaque (and easier to read) when the mouse hovers over it, you can use the :hover pseudo-class to change opacity to 1 on hover.
```
#caption:hover {
	opacity: 1;
}
```
Open the HTML page in a browser and hover your mouse over the caption to see it change.