/*

Self-referenced links, #permalinks, native lazy loading.

Each link pseudo-elements bleed 50% into the previous and next slide, acting as prev/next buttons, supplementing scroll/swipe, tab key (on focus), and keyboard arrows.

Alas, the image counter doesn‘t update on scroll ¯\_(ツ)_/¯

*/

html,
body {
  height: 100%;
}

.slideshow {
  height: 100%;
  overflow-x: scroll;
  scroll-snap-type: x mandatory;
  overscroll-behavior-x: contain;
  display: flex;
  gap: 4vw;
}

/* transition on :hover only so it doesn’t fire when opening a #permalink */
.slideshow:hover {
  scroll-behavior: smooth;
  /* `auto` for no transition on click/tab */
}

.slideshow figure {
  position: relative;
  scroll-snap-align: start;
  flex-shrink: 0;
  width: 100%;
  height: 100%;
  align-items: center;
  justify-content: center;
}

.slideshow figure a {
  flex-shrink: 0;
  width: 100%;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  -webkit-tap-highlight-color: transparent;
}

.slideshow a img {
  max-width: 100%;
  max-height: 100%;
  object-fit: contain;
  z-index: 1; /* cover the loading spinner */
}

.slideshow a:focus-visible {
  outline: 0;
}

/* Prev / Next */

.slideshow a:before,
.slideshow a:after {
  z-index: 2; /* cover the current image <a> */
  content: "";
  display: block;
  position: absolute;
  top: 0;
  bottom: 0;
  width: calc(50% + 4vw); /* 50vw + 4vw gap */
}

.slideshow a:before {
  left: calc(-1 * calc(50% + 4vw));
}

.slideshow a:after {
  right: calc(-1 * calc(50% + 4vw));
}

.slideshow :first-child a:before,
.slideshow :last-child a:after {
  display: none;
}

/* -- Loading spinner -- */

@keyframes spin {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}

.slideshow figure::after {
  content: "";
  height: 2em;
  width: 2em;
  animation: spin 0.8s infinite linear;
  border: 1px solid;
  border-right-color: transparent;
  border-radius: 50%;
  display: block;
  position: absolute;
  top: calc(50% - 1em);
  right: calc(50% - 1em);
  opacity: 0.4;
}

/* Counter */

.slideshow {
  counter-reset: currentStep 0 remainder 0 totalStep 0;
}

.slideshow figure {
  counter-increment: totalStep;
}

.slideshow figure::before {
  content: "";
  counter-increment: currentStep;
}

.slideshow figure:focus-within ~ figure::before {
  counter-increment: remainder;
}

.slideshow:hover figure:focus-within ~ .counter {
  z-index: 1;
  font-variant-numeric: tabular-nums;
  position: absolute;
  bottom: 1em;
  right: 1.5em;
  text-shadow: 1px 1px 1px #000;
}

.slideshow .counter::before {
  font-size: 0.9em;
  content: counter(currentStep) " / " counter(totalStep);
}

/* Demo styles */

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

a {
  text-decoration: none;
  color: currentColor;
}

body {
  font: 16px system-ui, sans-serif;
  background: #0e0e0f;
  color: #fff;
}