To set an opacity only to the background image of a div with CSS, we set the rgba value.
For instance, we write
div {
background-image: linear-gradient(
rgba(255, 255, 255, 0.5),
rgba(255, 255, 255, 0.5)
),
url("your_image.png");
}
to set the background-image of the div to a linear gradient with the rgba values.
0.5 is the opacity.
And we add the URL of the background image after the linear-gradient.