Transparent Image

The opacity property can take a value from 0.0 - 1.0. The lower value, the more transparent:

EXAMPLE:

img {
opacity: 0.5;
}

Transparent Hover Effect

The opacity property is often used together with the :hover selector to change the opacity on mouse-over:

EXAMPLE:

img {
opacity: 0.5;
}

img:hover {
opacity: 1.0;
}

Example explained

The first CSS block is similar to the code in Example 1. In addition, we have added what should happen when a user hovers over one of the images. In this case we want the image to NOT be transparent when the user hovers over it. The CSS for this is opacity:1;.

When the mouse pointer moves away from the image, the image will be transparent again.

An example of reversed hover effect:

EXAMPLE:

img:hover {
opacity: 0.5;
}

Transparent Box

When using the opacity property to add transparency to the background of an element, all of its child elements inherit the same transparency. This can make the text inside a fully transparent element hard to read:

EXAMPLE:

div {
opacity: 0.3;
}

Transparency using RGBA

If you do not want to apply opacity to child elements, like in our example above, use RGBA color values. The following example sets the opacity for the background color and not the text.

An RGBA color value is specified with: rgba(red, green, blue, alpha). The alpha parameter is a number between 0.0 (fully transparent) and 1.0 (fully opaque).

EXAMPLE:

div {
background: rgba(76, 175, 80, 0.3) /* Green background with 30% opacity */
}

Text in Transparent Box

EXAMPLE:

<html>
<head>
<style>
div.background {
background: url(klematis.jpg) repeat;
border: 2px solid black;
}

div.transbox {
margin: 30px;
background-color: #ffffff;
border: 1px solid black;
  opacity: 0.6;
}

div.transbox p {
  margin: 5%;
  font-weight: bold;
color: #000000;
}
</style>
</head>
<body>

<div class="background">
  <div class="transbox">
    <p>This is some text that is placed in the transparent box.</p>
  </div>
</div>

</body>
</html>