.cf img {
  position:absolute;
  left:0;
  -webkit-transition: opacity 1s ease-in-out;
  -moz-transition: opacity 1s ease-in-out;
  -o-transition: opacity 1s ease-in-out;
  transition: opacity 1s ease-in-out;
}

@-webkit-keyframes cfFadeInOut {
  0% {
  opacity:1;
}
45% {
opacity:1;
}
55% {
opacity:0;
}
100% {
opacity:0;
}
}

.cf img.top {
animation-name: cfFadeInOut;
animation-timing-function: ease-in-out;
animation-iteration-count: infinite;
animation-duration: 5s;
animation-direction: alternate;
}