add opacity to background image css. code example

Example 1: background-image: url opacity

background-image: url(IMAGE_URL); /* fallback for older browsers */

background-image: linear-gradient(to bottom, rgba(0,0,0,0.6) 0%,rgba(0,0,0,0.6) 100%), url(IMAGE_URL);

Example 2: set background image opacity

#bg{
background-image: url('images/wood1.jpg');
opacity:0.2;
width:300px;
height:300px;
}