#projects {
  background: url("../images/projects.jpg") no-repeat center/cover;
  position: relative;
  z-index: 1;
}

#projects::after {
  content: '';
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,0.5);
  z-index: -1;
}