.moving-image {
  position: relative;
  animation-name: slide;
  animation-duration: 1s;
  animation-timing-function: linear;
  animation-iteration-count: infinite;
  animation-direction: alternate;
}

@keyframes slide {
  0% {
    left: 300;
    transform: translateX(0);
  }
  100% {
    left: 400px;
    transform: translateX(0);
  }
}