adding overlay to a background image in css code example

Example 1: make background overlay css

#element-with-background-image {
   position: relative;
   background-image: url("//spin.atomicobject.com/wp-content/uploads/20170324102432/portfolio-tips-feature-image.jpg");
}
 
#color-overlay {
   position: absolute;
   top: 0;
   left: 0;
   width: 100%;
   height: 100%;
   background-color: black;
   opacity: 0.6;
}

Example 2: how to add a background overlay in css

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