style.scss

$zoom-z-index: 2000 !default;

$zoom-transition-duration: 300ms !default;
$zoom-transition-timing-function: cubic-bezier(0.2, 0, 0.2, 1) !default;

$zoom-overlay-z-index: 1000 !default;
$zoom-overlay-background-color: hsl(0, 0%, 100%) !default;
$zoom-overlay-visible-opacity: 100 !default;

.zoom,
.zoom__overlay,
.zoom__container,
.zoom__image,
.zoom__clone {
  display: block;
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

.zoom {
  position: relative;
  width: 100%;

  margin: {
    left: auto;
    right: auto;
  }
}

.zoom--expanding,
.zoom--expanded,
.zoom--collapsing {
  z-index: $zoom-z-index;
}

.zoom__container {
  position: relative;
  transition: transform $zoom-transition-duration $zoom-transition-timing-function;
  will-change: transform;
}

.zoom__image,
.zoom__clone {
  cursor: pointer;
  cursor: -moz-zoom-in;
  cursor: -webkit-zoom-in;

  margin: auto;
  backface-visibility: hidden;
}

.zoom__image--active,
.zoom__clone--visible {
  cursor: pointer;
  cursor: -moz-zoom-out;
  cursor: -webkit-zoom-out;
}

.zoom__image--hidden,
.zoom__clone {
  visibility: hidden;
  opacity: 0;
  transition: visibility 0s linear 500ms, opacity 100ms 400ms;
}

.zoom__image,
.zoom__clone--visible {
  visibility: visible;
  opacity: 1;
  transition: visibility 0s linear 0s, opacity 400ms 0s;
}

.zoom__image {
  max-width: 100%;
}

.zoom__image--active {
  width: 100%;
}

.zoom__clone {
  position: absolute;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;

  width: 100%;
}

.zoom__overlay {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;

  z-index: $zoom-overlay-z-index;
  background: $zoom-overlay-background-color;

  opacity: 0;
  filter: 'alpha(opacity=0)';
  transition: opacity $zoom-transition-duration;
  will-change: opacity, filter;
}

.zoom__overlay--visible {
  opacity: $zoom-overlay-visible-opacity / 100;
  filter: 'alpha(opacity=#{$zoom-overlay-visible-opacity})';
}