What is Opacity in Css?

Question

how will it appear in Gecko, WebKit and IE.

Answer 1

The opacity property in CSS specifies how transparent an element is. Opacity has a default initial value of 1 (100% opaque) and Opacity is not inherited.
Values are a number from 0 to 1 representing the opacity of the channel on the scale of 0 to 100%

Example:

img {
    opacity: 0.5;
    filter: alpha(opacity=50); /* For IE8 and earlier */
}

img:hover {
    opacity: 1.0;
    filter: alpha(opacity=100); /* For IE8 and earlier */
}

in the above example image has the opacity as 50% and whenever we hover it becomes 100% opaque.

Answer 2

Opacity determines the Transparency of an element in CSS. The value of opacity lies between 0.0 to 1. The less the value, the more Transparent it would be.The default value of opacity is 1.