.slider
{
  
  overflow: hidden;
  width: 100%;
  float: left;
  z-index: -100;
}

.slider ul
{
    padding: 0;
    display: flex;
    width: 300%;
    animation: cambio 20s infinite alternate linear; 
    
}

.slider li
{
  width: 100%;
  list-style: none;
  font-size: 20px;
}

.slider img
{
  width: 100%;
  height: 100%;
}

.slider .contenedor
{
  position: absolute;
  top: 50%;
  left: 50%; 
  transform: translateX(-50%) translateY(-50%);
  color: #fff;

}


@keyframes cambio
{
  0% {margin-left: 0;}
  30% {margin-left: 0;}

  35% {margin-left: -100%;}
  65% {margin-left: -100%;}
  
  70% {margin-left: -200%;}
  100% {margin-left: -200%;}
  
}