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A (CSS) Horse of a Different Color - Part 2

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In addition to the RGBA and HSLA color values, the draft CSS3 color also adds an additional transparent value (i.e. "color: transparent") to all Web objects capable of taking a color value. So, when you add this value to an object, you render it fully transparent, although it is still "there". This was a value that previously could only be applied to the background-color property, but this new arrangement simplifies things considerably, making it easier to directly – and dynamically, using JavaScript – change the transparency of a Web object.

Opacity

The RGBA and HSLA color values allow you to set transparency values to the colors you specify. But the draft CSS3 color module goes further, allowing you to set transparency values without the need to set a color value along with them. So in other words, you can set the relative opacity of other objects – like images – as well. This has the potential to let Web developer create some interesting blending effects.

Like the RGBA and HSLA color values, the opacity property would take a decimal value ranging from 0.0 (fully transparent) to 1.0 (fully opaque), with any value greater or lower than this clipped so that it stays within this range. The opacity value is applied across the entire element – any outline, border or background that may be associated with a selected element are all rendered using the same opacity value.

The following sample code shows how it could be used, whose results should show headers that are increasingly transparent:

<html>
<head>
<title>opacity Example</title>
<style>
h1 {font-size: x-large}
.opaque {opacity: 1.0}
.point-eight-opaque {opacity: 0.8}
.point-six-opaque {opacity: 0.6}
.point-four-opaque {opacity: 0.4}
.point-two-opaque (opacity: 0.2)
.transparent {opacity: 0.0}
</style>
</head>
<body>
<h1 class="opaque">This header is fully opaque</h1>
<h1 class="point-eight-opaque">This header is set to 0.8 opacity</h1>
<h1 class="point-six-opaque">This header is set to 0.6 opacity</h1>
<h1 class="point-four-opaque">This header is set to 0.4 opacity</h1>
<h1 class="point-two-opaque">This header is set to 0.2 opacity</h1>
<h1 class="transparent">This header is fully transparent</h1>
Some extra text to display the effects of the transparent header.
</body>
</html>

You can see the effects of this illustrated in the following mock-up:



While the code example provided here are being applied to headers; unlike the previous RGBA and HSLA code samples, the opacity property could be directly applied to virtually anything, including such things as other text blocks, images, user interface controls (i.e. buttons) and more.

Please keep in mind that all of these properties are still (at the time of writing) not finalized in the CSS3 color module. So while things may be different in the final version of the specification, this still provides an idea as to what to expect in future browsers.

Compiled by Keith Schengili-Roberts

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Created: March 27, 2003
Revised: June 17, 2003

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