Description

Opacity sets the transparency of an element, including background, text and border.
It accepts values from 0.0 fully transparent to 1.0 fully opaque.
A similar effect that only applies to color and background-color can be achieved using the alpha transparency of rgba color eg background-color:rgba(0, 255, 0, 0.5);
Versions of IE 8 and earlier needed the proprietary filter property eg filter:alpha(opacity=40);

Live Example
Play with the code in the textarea below.

Values
0.0 to 1.0
Default value
1
Introduced in CSS version
3
Applies to elements
All
Inherited
No
Browser Support
BrowsersIEFirefoxSafariOperaChrome
Versions93.6511.617
Belongs to:

See the full list CSS properties and browser support: CSS Properties