section div {
  transition-property: transform, opacity;
  transition-duration: 0.3s;
  opacity: 0;
}
section:nth-child(even) div {
  transform: translateX(-100%);
}
section:nth-child(odd) div {
  transform: translateX(100%);
}
section.visible div {
  transform: none;
  opacity: 1;
}