opacity()

Controls how much of the background is visible through the element it is applied to.

filter: opacity(<value>);

where a required <value> can be one of the following:

• Number value: 0, 1
• Percentage value: 25%, 50%

Note: Value defaults to 1 or 100% leaving element unchanged. A value of 0 and 0% will be completely transparent. Negative values as well as values greater than 1 or 100% are not allowed.

Set the opacity of our element to 50%:

.banner-image {
  filter: opacity(50%);
}