CSS Code
Output
<!DOCTYPE html>
<html>
<head>
<style>
.slideshow {
  position: absolute;
  width: 100vw;
  height: 100vh;
  overflow: hidden;
}

.slideshow-image {
  position: absolute;
  width: 100%;
  height: 100%;
  background: no-repeat 50% 50%;
  background-size: cover;
  -webkit-animation-name: kenburns;
          animation-name: kenburns;
  -webkit-animation-timing-function: linear;
          animation-timing-function: linear;
  -webkit-animation-iteration-count: infinite;
          animation-iteration-count: infinite;
  -webkit-animation-duration: 10s;
          animation-duration: 10s;
  opacity: 1;
  -webkit-transform: scale(1.2);
          transform: scale(1.2);
}
.slideshow-image:nth-child(1) {
  -webkit-animation-name: kenburns-1;
          animation-name: kenburns-1;
  z-index: 4;
}
.slideshow-image:nth-child(2) {
  -webkit-animation-name: kenburns-2;
          animation-name: kenburns-2;
  z-index: 3;
}
.slideshow-image:nth-child(3) {
  -webkit-animation-name: kenburns-3;
          animation-name: kenburns-3;
  z-index: 2;
}
.slideshow-image:nth-child(4) {
  -webkit-animation-name: kenburns-4;
          animation-name: kenburns-4;
  z-index: 1;
}
.slideshow-image:nth-child(5) {
  -webkit-animation-name: kenburns-5;
          animation-name: kenburns-5;
  z-index: 0;
}

@-webkit-keyframes kenburns-1 {
  0% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  5% {
    opacity: 1;
  }
  15% {
    opacity: 1;
  }
  25% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  95% {
    opacity: 0;
    -webkit-transform: scale(1.24);
            transform: scale(1.24);
  }
  100% {
    opacity: 1;
  }
}

@keyframes kenburns-1 {
  0% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  5% {
    opacity: 1;
  }
  15% {
    opacity: 1;
  }
  25% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  95% {
    opacity: 0;
    -webkit-transform: scale(1.24);
            transform: scale(1.24);
  }
  100% {
    opacity: 1;
  }
}
@-webkit-keyframes kenburns-2 {
  15% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  25% {
    opacity: 1;
  }
  35% {
    opacity: 1;
  }
  45% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
}
@keyframes kenburns-2 {
  15% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  25% {
    opacity: 1;
  }
  35% {
    opacity: 1;
  }
  45% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
}
@-webkit-keyframes kenburns-3 {
  35% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  45% {
    opacity: 1;
  }
  55% {
    opacity: 1;
  }
  65% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
}
@keyframes kenburns-3 {
  35% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  45% {
    opacity: 1;
  }
  55% {
    opacity: 1;
  }
  65% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
}
@-webkit-keyframes kenburns-4 {
  55% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  65% {
    opacity: 1;
  }
  75% {
    opacity: 1;
  }
  85% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
}
@keyframes kenburns-4 {
  55% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  65% {
    opacity: 1;
  }
  75% {
    opacity: 1;
  }
  85% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
}
@-webkit-keyframes kenburns-5 {
  75% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  85% {
    opacity: 1;
  }
  95% {
    opacity: 1;
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
}
@keyframes kenburns-5 {
  75% {
    opacity: 1;
    -webkit-transform: scale(1.2);
            transform: scale(1.2);
  }
  85% {
    opacity: 1;
  }
  95% {
    opacity: 1;
  }
  100% {
    opacity: 0;
    -webkit-transform: scale(1);
            transform: scale(1);
  }
}
h1 {
  position: absolute;
  top: 50%;
  left: 50%;
  -webkit-transform: translate3d(-50%, -50%, 0);
          transform: translate3d(-50%, -50%, 0);
  z-index: 99;
  text-align: center;
  font-family: Raleway, sans-serif;
  font-weight: 300;
  text-transform: uppercase;
  background-color: rgba(255, 255, 255, 0.75);
  box-shadow: 0 1em 2em -1em rgba(0, 0, 0, 0.5);
  padding: 1em 2em;
  line-height: 1.5;
}
h1 small {
  display: block;
  text-transform: lowercase;
  font-size: .7em;
}
h1 small:first-child {
  border-bottom: 1px solid rgba(0, 0, 0, 0.25);
  padding-bottom: .5em;
}
h1 small:last-child {
  border-top: 1px solid rgba(0, 0, 0, 0.25);
  padding-top: .5em;
}

</style>
</head>
<body>

<h1>A demo of slideshow with background images without JS:  Ken Burns effect </h1>


<div class="slideshow">
  <div class="slideshow-image" style="background-image: url('https://www.jquery-az.com/jquery/images/slider-image-1.jpg')"></div>
  <div class="slideshow-image" style="background-image: url('https://www.jquery-az.com/jquery/images/slider-image-2.jpg')"></div>
  <div class="slideshow-image" style="background-image: url('https://www.jquery-az.com/jquery/images/slider-image-1.jpg')"></div>
  <div class="slideshow-image" style="background-image: url('https://www.jquery-az.com/jquery/images/banana.jpg')"></div>
  <div class="slideshow-image" style="background-image: url('https://www.jquery-az.com/jquery/images/banana.jpg')"></div>
</div>
</body>
</html>
A demo of slideshow with background images without JS: Ken Burns effect
