@keyframes slider {
0%  {left: 0;}
20% {left: 0;}
25% {left: -100%;}
45% {left: -100%;}
50% {left: -200%;}
70% {left: -200%;}
75% {left: -300%;}
95% {left: -300%;}
100% {left: -400%;}
}
#slider {
  overflow: hidden;
  margin: auto;
  max-width: 1200px;
  position: relative;
  padding-top: 42.86%;
}
#slider figure img {
  width: 20%;
  float: left;
}
#slider figure {
  position: absolute;
  top: 50%;
  width: 500%;
  margin: 0;
  -ms-transform: translateY(-50%);
  transform: translateY(-50%);
  animation: 16s slider infinite; 
}