Bootstrap/scss/_carousel.scss

// Wrapper for the slide container and indicators
.carousel {
  position: relative;
}

.carousel-inner {
  position: relative;
  width: 100%;
  overflow: hidden;

  > .carousel-item {
    position: relative;
    display: none;
    transition: .6s ease-in-out left;

    // Account for jankitude on images
    > img,
    > a > img {
      @extend .img-fluid;
      line-height: 1;
    }

    // CSS3 transforms when supported by the browser
    @include if-supports-3d-transforms() {
      transition: transform .6s ease-in-out;
      backface-visibility: hidden;
      perspective: 1000px;

      &.next,
      &.active.right {
        left: 0;
        transform: translate3d(100%, 0, 0);
      }
      &.prev,
      &.active.left {
        left: 0;
        transform: translate3d(-100%, 0, 0);
      }
      &.next.left,
      &.prev.right,
      &.active {
        left: 0;
        transform: translate3d(0, 0, 0);
      }
    }
  }

  > .active,
  > .next,
  > .prev {
    display: block;
  }

  > .active {
    left: 0;
  }

  > .next,
  > .prev {
    position: absolute;
    top: 0;
    width: 100%;
  }

  > .next {
    left: 100%;
  }
  > .prev {
    left: -100%;
  }
  > .next.left,
  > .prev.right {
    left: 0;
  }

  > .active.left {
    left: -100%;
  }
  > .active.right {
    left: 100%;
  }
}


//
// Left/right controls for nav
//

.carousel-control {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  width: $carousel-control-width;
  font-size: $carousel-control-font-size;
  color: $carousel-control-color;
  text-align: center;
  text-shadow: $carousel-text-shadow;
  opacity: $carousel-control-opacity;
  // We can't have this transition here because WebKit cancels the carousel
  // animation if you trip this while in the middle of another animation.

  // Set gradients for backgrounds
  &.left {
    @include gradient-x($start-color: rgba(0,0,0,.5), $end-color: rgba(0,0,0,.0001));
  }
  &.right {
    right: 0;
    left: auto;
    @include gradient-x($start-color: rgba(0,0,0,.0001), $end-color: rgba(0,0,0,.5));
  }

  // Hover/focus state
  @include hover-focus {
    color: $carousel-control-color;
    text-decoration: none;
    outline: 0;
    opacity: .9;
  }

  // Toggles
  .icon-prev,
  .icon-next {
    position: absolute;
    top: 50%;
    z-index: 5;
    display: inline-block;
    width: $carousel-icon-width;
    height: $carousel-icon-width;
    margin-top: -($carousel-icon-width / 2);
    font-family: serif;
    line-height: 1;
  }
  .icon-prev {
    left: 50%;
    margin-left: -($carousel-icon-width / 2);
  }
  .icon-next {
    right: 50%;
    margin-right: -($carousel-icon-width / 2);
  }

  .icon-prev {
    &::before {
      content: "\2039";// SINGLE LEFT-POINTING ANGLE QUOTATION MARK (U+2039)
    }
  }
  .icon-next {
    &::before {
      content: "\203a";// SINGLE RIGHT-POINTING ANGLE QUOTATION MARK (U+203A)
    }
  }
}


// Optional indicator pips
//
// Add an unordered list with the following class and add a list item for each
// slide your carousel holds.

.carousel-indicators {
  position: absolute;
  bottom: 10px;
  left: 50%;
  z-index: 15;
  width: $carousel-indicators-width;
  padding-left: 0;
  margin-left: -($carousel-indicators-width / 2);
  text-align: center;
  list-style: none;

  li {
    display: inline-block;
    width: $carousel-indicator-size;
    height: $carousel-indicator-size;
    margin: 1px;
    text-indent: -999px;
    cursor: pointer;
    // IE9 hack for event handling
    //
    // Internet Explorer 9 does not properly handle clicks on elements with a `background-color` of `transparent`,
    // so we use `rgba(0,0,0,0)` instead since it's a non-buggy equivalent.
    // See https://developer.mozilla.org/en-US/docs/Web/Events/click#Internet_Explorer
    background-color: rgba(0,0,0,0); // IE9
    border: 1px solid $carousel-indicator-border-color;
    border-radius: $carousel-indicator-size;
  }

  .active {
    width: $carousel-indicator-active-size;
    height: $carousel-indicator-active-size;
    margin: 0;
    background-color: $carousel-indicator-active-bg;
  }
}


// Optional captions
//
// Hidden by default for smaller viewports.

.carousel-caption {
  position: absolute;
  right: ((100% - $carousel-caption-width) / 2);
  bottom: 20px;
  left: ((100% - $carousel-caption-width) / 2);
  z-index: 10;
  padding-top: 20px;
  padding-bottom: 20px;
  color: $carousel-caption-color;
  text-align: center;
  text-shadow: $carousel-text-shadow;

  .btn {
    text-shadow: none; // No shadow for button elements in carousel-caption
  }
}


//
// Responsive variations
//

@include media-breakpoint-up(sm) {
  // Scale up the controls a smidge
  .carousel-control {
    .icon-prev,
    .icon-next {
      width: $carousel-control-sm-up-size;
      height: $carousel-control-sm-up-size;
      margin-top: -($carousel-control-sm-up-size / 2);
      font-size: $carousel-control-sm-up-size;
    }
    .icon-prev {
      margin-left: -($carousel-control-sm-up-size / 2);
    }
    .icon-next {
      margin-right: -($carousel-control-sm-up-size / 2);
    }
  }

  // Show and left align the captions
  .carousel-caption {
    right: ((100% - $carousel-caption-sm-up-width) / 2);
    left: ((100% - $carousel-caption-sm-up-width) / 2);
    padding-bottom: 30px;
  }

  // Move up the indicators
  .carousel-indicators {
    bottom: 20px;
  }
}