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Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Color alpha controls how transparent a color is: 0 (or 0%) is fully transparent, and 1 (or 100%) is fully opaque. In CSS, putting alpha in a color makes that color translucent; the opacity property instead fades the rendered element and its descendants.
What does alpha mean in a color?
Alpha is the opacity component associated with a color. In an RGBA color, the RGB components describe red, green, and blue, while alpha specifies how opaque that color appears. The W3C describes alpha as extending the RGB color model to allow specification of a color’s opacity in its RGBA reference.
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CSS alpha values use a scale from 0 to 1, or the equivalent percentage scale: 0 or 0% is fully transparent; 1 or 100% is fully opaque. Values in between are translucent. See MDN’s definition of the <alpha-value> CSS type.
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How do you make a color transparent in CSS?
Use a color function with an alpha value. In modern CSS rgb() syntax, a slash separates the RGB components from alpha. If you omit alpha, the color is fully opaque.
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.card {
/* Only the background color is translucent. */
background-color: rgb(30 100 220 / 50%);
}Here, the background color is 50% opaque, allowing what is behind that background to show through. The RGB values identify the color; the percentage after the slash sets its alpha. MDN documents this syntax and the default opaque value in its rgb() reference.
Change only a reusable color’s alpha
The CSS alpha() function can derive a variant of an existing color while changing its alpha, rather than restating its other color components. For example:
.card {
background-color: alpha(from var(--brand-color) / 50%);
}MDN marks alpha() browser availability as newly available across the latest devices and browser versions in September 2026. Older devices may not support it, so check support for your target browsers before relying on it in production.
Color alpha versus the CSS opacity property
The distinction is the scope of the effect. Alpha belongs to a color value; CSS opacity applies to the rendered element as a whole, including its descendants. The W3C describes element opacity as postprocessing applied to the rendered element and its descendants in CSS Color Module Level 3.
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| Approach | What becomes translucent | Example |
|---|---|---|
| Alpha in a color | That color only | background-color: rgb(30 100 220 / 50%); |
| Element opacity | The rendered element and its descendants | opacity: 0.5; |
Use color alpha when you want, for example, a translucent background while keeping text and child elements fully opaque. Use opacity when the intended effect is to fade the entire rendered element, including its contents.
.card-faded {
/* The whole rendered element, including descendants, is translucent. */
opacity: 0.5;
}What is premultiplied alpha?
Premultiplied alpha is a way of representing color data in which each color component is multiplied by the alpha value. This is an implementation detail that matters when working with image or graphics data: a pipeline may expect premultiplied or non-premultiplied channel values, and the two representations should not be treated as interchangeable.
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Converting between premultiplied and non-premultiplied values can lose precision for non-opaque colors, as described in the WHATWG HTML Standard. When transferring image data between APIs or processing stages, check which representation each stage expects to avoid incorrect conversions.
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