@keyframes loader {
  0% {
    width: 50px;
    height: 50px;
    top: calc(50% - 25px);
    left: calc(50% - 25px);
    opacity: 1;
  }
  80% {
    width: 100px;
    height: 100px;
    top: calc(50% - 50px);
    left: calc(50% - 50px);
    opacity: 0;
  }
  100% {
    width: 50px;
    height: 50px;
    top: calc(50% - 25px);
    left: calc(50% - 25px);
    opacity: 0;
  }
}

#loader {
  display: none;
  position: fixed;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  background: #f3f3f4;
  z-index: 9;
}
#loader span {
  display: block;
  position: absolute;
  width: 50px;
  height: 50px;
  top: calc(50% - 25px);
  left: calc(50% - 25px);
  border: 2px solid rgba(119, 119, 119, .75);
  border-radius: 50%;
  -webkit-box-shadow: 0px 0px 3px 1px rgba(119,119,119,1);
  -moz-box-shadow: 0px 0px 3px 1px rgba(119,119,119,1);
  box-shadow: 0px 0px 3px 1px rgba(119,119,119,1);
  animation: loader 1000ms ease-out infinite;
}