.loader {
  position: absolute;
}

.loader:before {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  display: block;
  width: 5em;
  height: 0.5em;
  border-radius: 0.5em;
  transform: translate(-50%, -50%);
  animation: slide 2.5s infinite;
}

@keyframes slide {
  0% {
    width: 5em;
    box-shadow:
      1em -0.5em #2b546b,
      -1em 0.5em #aabbc4;
  }

  35% {
    width: 0.5em;
    box-shadow:
      0 -0.5em #2b546b,
      0 0.5em #aabbc4;
  }

  70% {
    width: 0.5em;
    box-shadow:
      -1em -0.5em #2b546b,
      1em 0.5em #aabbc4;
  }

  100% {
    width: 5em;
    box-shadow:
      1em -0.5em #2b546b,
      -1em 0.5em #aabbc4;
  }
}