<div class="gallery">
  <div class="gallery__prev"></div>
  <div class="gallery__next"></div>
  <div class="gallery__stream">
    <div class="gallery__item bg-1"></div>
    <div class="gallery__item bg-2"></div>
    <div class="gallery__item bg-3"></div>
    <div class="gallery__item bg-4"></div>
    <div class="gallery__item bg-5"></div>
    <div class="gallery__item bg-6"></div>
    <div class="gallery__item bg-7"></div>
  </div>
</div>

/* Global */

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  background-color: #000;
}

/* Gallery */

.gallery {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
  width: 100%;
  height: 90%;
  max-height: 28vw;
  overflow: hidden;
}

.gallery:before,
.gallery:after {
  display: block;
  content: "";
  position: absolute;
  top: 0;
  width: 20%;
  height: 100%;
  z-index: 3;
}

.gallery:before {
  left: 0;
  background:  linear-gradient(to right, rgba(0,0,0,1) 0%, rgba(0,0,0,0) 100%);
}

.gallery:after {
  right: 0;
  background:  linear-gradient(to left, rgba(0,0,0,1) 0%, rgba(0,0,0,0) 100%);
}

.gallery__stream {
  position: relative;
  top: 50%;
  transform: translateY(-50%);
  width: 100%;
  height: 100%;
}

.gallery__item {
  position: absolute;
  width: 50%;
  height: 100%;
  transition: 1s all ease;
  background-size: cover;
  background-repeat: no-repeat;
  background-position: center center;
  border-radius: 5px;
}

.gallery__item:nth-child(1) {
  left: 0;
  z-index: 1;
  transform: translateX(-100%) scale(.8);
}

.gallery__item:nth-child(2) {
  left: 0;
  z-index: 2;
  transform: translateX(-50%) scale(.8);
}

.gallery__item:nth-child(3) {
  left: 50%;
  z-index: 4;
  transform: translateX(-50%) scale(1);
}

.gallery__item:nth-child(4) {
  left: 100%;
  z-index: 2;
  transform: translateX(-50%) scale(.8);
}

.gallery__item:nth-child(n+5) {
  left: 100%;
  z-index: 1;
  transform: scale(.8);
}

/* Controllers */

.gallery__prev,
.gallery__next {
  position: absolute;
  top: 50%;
  z-index: 4;
  width: 50%;
  height: 100%;
  transform: translateX(-50%) translateY(-50%) scale(.8);
  cursor: pointer;
}

.gallery__prev {
  left: 0;
}

.gallery__next {
  left: 100%;
}

/* Backgrounds */

.bg-1 {
  background-image: url(https://res.cloudinary.com/dm7h7e8xj/image/upload/v1554487589/star-wars-1_kgt8dr.jpg);
}

.bg-2 {
  background-image: url(https://res.cloudinary.com/dm7h7e8xj/image/upload/v1554487590/star-wars-2_tgzyxe.jpg);
}

.bg-3 {
  background-image: url(https://res.cloudinary.com/dm7h7e8xj/image/upload/v1554487591/star-wars-3_bkcmeb.jpg);
}

.bg-4 {
  background-image: url(https://res.cloudinary.com/dm7h7e8xj/image/upload/v1554487591/star-wars-4_opgyza.jpg);
}

.bg-5 {
  background-image: url(https://res.cloudinary.com/dm7h7e8xj/image/upload/v1554487591/star-wars-5_ulc9tx.jpg);
}

.bg-6 {
  background-image: url(https://res.cloudinary.com/dm7h7e8xj/image/upload/v1554487591/star-wars-6_la8whc.jpg);
}

.bg-7 {
  background-image: url(https://res.cloudinary.com/dm7h7e8xj/image/upload/v1554487590/star-wars-7_l3fcor.jpg);
}

document.addEventListener('DOMContentLoaded', function() {
  var stream = document.querySelector('.gallery__stream');
  var items = document.querySelectorAll('.gallery__item');
  
  var prev = document.querySelector('.gallery__prev');
  prev.addEventListener('click', function() {
    stream.insertBefore(items[items.length - 1], items[0]);
    items = document.querySelectorAll('.gallery__item');
  });
  
  var next = document.querySelector('.gallery__next');
  next.addEventListener('click', function() {
    stream.appendChild(items[0]);
    items = document.querySelectorAll('.gallery__item');
  });
});