overlay black on image css code example

Example 1: how to put a black overlay on a photo css

.header {
  background: rgba(0, 0, 0, 0.5); /* Black color with 50% alpha/opacity */
}

Example 2: overlay color on image css

footer#site-footer{  
  position:relative;
}

footer#site-footer:before {     /* use before property (pseudo-element)  */
    position: absolute;
    content: '';
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.3);
}