.carousel {
  width: 70%;
  overflow: hidden;
}

.track {
  display: flex;
  width: 200%; /* 3 images */
  animation: slide 6s infinite;
}

.track img {
  width: 50%; /* each image is 1/3 of the track */
  display: block;
}

@keyframes slide {
  0%   { transform: translateX(0); }
  33%  { transform: translateX(-50%); }
  100% { transform: translateX(0); }
}