@keyframes slide {
  from {
    -moz-transform: translateX(0);
    -webkit-transform: translateX(0);
    transform: translateX(0)
  }
  to {
    -moz-transform: translateX(-800px);
    -webkit-transform: translateX(-800px);
    transform: translateX(-800px);
  }
}

#slider {
  max-width: 800px;
  width: 100%;
  max-height: 600px;
  display: inline-block;
}
.slide {
  -moz-animation:     slide 1.5s ease-in-out 2s 1 alternate;
  -webkit-animation:  slide 1.5s ease-in-out 2s infinite alternate;
  animation:          slide 25s linear infinite;
  max-width: 800px;
  width: 100%;
  max-height: 600px;
}