The opacity property

The opacity property sets a transparency of an element. If the element is set to transparent, this means that the elements that lie underneath will be visible through it.

The property takes a fractional number from 0 to 1 as its value. In this case, the 0 value is complete transparency, and the 1 value is complete opacity. An intermediate value, for example 0.3, sets the half transparency. Default value: 1.

Syntax

selector {
	opacity: number from 0 to 1;
}

Example

In this example, transparency is added to a block and the background of the parent is visible through a border and a text of this block:

<div id="parent">
	<div id="elem">
		Lorem ipsum dolor sit amet.
	</div>
</div>

#parent {
	background-image: url("bg.png");
	background-repeat: no-repeat;
	background-size: cover;
	display: inline-block;
	padding: 30px;
}
#elem {
	width: 300px;
	height: 200px;
	border: 20px solid red;
	padding: 10px;
	font-size: 50px;
	font-weight: bold;
	color: red;
	background: black;
	opacity: 0.7;
}