loading-spinner {
    display: block;
    position: absolute;
    bottom: 0;
    left: 0;
    right: 0;
    z-index: 1;
    opacity: 0.3;
    height: 10px;
}

loading-spinner::before {
  position: absolute;
  content: "";
  width: 10px;
  height: 100%;
  top: 0;
  left: 0;
  animation-name: loadingAnimation;
  animation-duration: 1s;
  animation-iteration-count: infinite;
  background-color: blue;
}

@keyframes loadingAnimation {
  0% {
    left: 0;
  }
  100% {
    left: calc(100% - 10px);
  }
}