#loader {
  display: none;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, 0.5);
  z-index: 9998;
}

#loader > .spinner-border{
  position: absolute;
  top: 50%;
  left: 50%;
}