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

cssselector {
  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:

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

css#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;
}

Результат: