body::before{
content: "";
position: absolute;
top: 0;
right: 0;
bottom: 0;
left: 0;
z-index: -1;
background-image: url(image.jpg); /*Put your image url*/
background-size: cover;
background-position: center;
opacity: 0.25; /*Value from 0.0 to 1.0*/
}
/* Two ways to make images opaque */
div {
background-color : rgba(120, 120, 120, 0.5)
/* the 0.5 is the value of opacity on a scale of 0-1 */
}
/* OR */
div {
background-color : blue
opacity : 50%
}
div {
opacity : 50%;
}
/* Use opacity to change the opacity of selected css */