background-image:url(https://i.ytimg.com/vi/Gyd6Y6gsv9c/hqdefault.jpg) 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: background image

div {
  background-color: #ffffff;
  background-image: url("img_tree.png");
  background-repeat: no-repeat;
  background-attachment: scroll|fixed|local|initial|inherit;
  background-position: right top  |  x% y%  |  xpos ypos;
  background-clip: border-box|padding-box|content-box|initial|inherit;
  background-size: auto|length|cover|contain|initial|inherit;
}
//shorthand:
div {
  background: #ffffff url("img_tree.png") no-repeat right top;
}