- var images = ["https://lh3.googleusercontent.com/aC9nyW5dhaYFmWD8fcf8DApjpH08eHEkbCHqmUPHRQ5T3jK-QyNKZYVMehmrvyPdEA_KxWvgZ3_kyOOYOAv99Ow3UoKSvEloleVKGSfLOwOyDV3Q6Dwi1G-NYoa9-t_ofmmskE6BYnVIOnIz2HWlMcijzIEwvKAL_R4z63DaLgG0z_OcGiSQHunwGAPXrBQUv42ZXuIMODq4zxDHczSxJ72b0-_udtdQK3JuT2X8nXCwFoF7GxmOpzXS0H5f50DuCbXoXcx-O7bgBMCXZdMpTxB27-wdXeLmxpYUySXgjSN2NAKmK16DmGLYvw5tMlrqwb8h4MJEEbXjP1pjPxXsahb7UZseEGyn80uLjATANJvusyJWCtzkkxYXPz-yI1rDvfEJKe2eyA-5AvFlzFBSwBMASn8f7mXinUrXMMREkJQjoi89NfZ91G7253OEVQOqcWxddiYtcHCO5v6Pl3QfV2SUTWXgggscDSY2ezjSPpYERNTXnIM_aCyWmIG7ybrfqOB0eVYBAgynyuPVbjd4KuZWZq2Dfu33HX1RuPKglbOuZGD1QbpJnruvUVkAmjDXI40ENN7X=w1600-h766","https://lh3.googleusercontent.com/4Bn4zdADhWhegRcmxS1xmHxbxIBzEgB8ADfeaCmiwT9iF7y2mN9Wc5L7gFLxUo2bgl3V-97EFrOyE9OXfkvip3pkpNxYe50GiapeT41p7D7tNJm3oEdV8Y-7toGyvz0UZ8VgDACVTUEdzzVVm2NtQSCroSvmo4gL3u0ty-KAyKnah9vIitfw2Rs1MuNzQq6vmzUcw1_4obGAKmk_Nx0dD33RSy1jbT8D61kxERbOu0pHUciywIO2EeUX8iOcJfHHQwVW3lGYcZKSiimGjBUvzHILrSpVZQ1xUlj0U21EeY4Hil1ZaJQaX47hQezcxZj7H8GyWhNv2TzQ7EU8DS3_MonCLxXlnXfk-80nncPa8DxN_UlIzJeOPDiWPSLXFaDJn_ywCutx-0onw5rcSC815_krGHXKt3L_weD5pq_e_2WI3BRZndcR2jOYLz9BiUp52ouDBIDw2OzrDtUgxne9NaQ2tOJwaIR26N1un92ChTLhXZF2F2NoS3Do96TY6A5dP6RsXQzK6G0Z6oj5XtYx-p--PrdP8wiDPAzOqXQkXbJaX8l2qPi3nTYrD8rB-eKyL2E1q9xQ=w1600-h766","https://lh3.googleusercontent.com/r29_BOXT9GjEA49-KbPtzHtTxD16dilHpFROmoJyZdQbvCelXqgG8bcApe8OgIY-avTrFOUWO-lDsmI-muMIgRVc5IFHCIyrOR18DrnwTLh70aSNY6cTY0bNbyt4QCXBlj9R4fmA8PJMRYkTA-nB5zSvlZii9NnP9kG8w__DUrYfo9IbOZAxGY_DsheGuHA0CSWLB-lQwvHo7_sSNabsiZJ2C_878r7uEfaIR6XkjcyrWMKi529UtPl9Ikln3cXphy9HrzElIL6200dGL9GHiMMoASseLp_Z950xjT2smzTrOJSADFCG9EmScicKDbFTYZH6gyc2DEP0mUFRArhTSPa4TIUwLy9KR8bG7kV-ljmSPKv4pbtH4ByXgQ5DEm5ydOkR-DTkYkLBkcFL8cjiBPPuUdK3xkjoOciwjglMF5xAXhpnTj0VUnk3RWc9YDD-AQI2uvDatV_Ae0zzLQUIm2gfV3QiDXdkkzeLWsRmCXrr0bFf42s_1NrWD0GLfrTtHNqzBCfYbAWtjeBxHfMxlESqJLAvGketLMscx5PndptC0MRhGZESjWdRUE3kNxg7PA9EhTZg=w1600-h766","https://lh3.googleusercontent.com/7MsdX710gvwl8YRxuiPIlIbGP8d3ypDASWqIOad9SpHHAPwMATjCoftyvoHjpy9eeD8aJVxVup-Zb02QMeBSFOXyqOlVc8ib3TVIXtktozy6sJK07H8Jo8UlJSpYcfgUq83Z5rJOiGQQAaZPhRYUcCR0aenU8Eh8aTuqvttfZA-PjsU39q5_I1HcpWDF1mXIxJTmlGqsoQNIuL75GDE-I2im2tAjEk6bkJkJEbDntxB5cLJEfV8TuKRsQwenkiN5opF4ttHGXYtJlS7adu-IO4wVIFcEOzdx4c1Eri3O6f9qjsTpXQH3BmpkTaLAtL5xzJit9qa0a4Dp-aZOZp1QzWeB6-dLM5HRxSiPFkku3S1umwm_GBeY3glxd3Ftata1mFIxpis6gR76oTiNO33vjxn1UZXYhCQUDByGyyuE6WOoPtu9iXJxfmUF9UMXiXVl7qyH-U7NJmq18qcU0Q6U7H3VucD_d2Vg8WTZmqVq7aA4jQ7MLuQASgMZIerxgwV_aW98z7xsS8isHgF9rN4Qtez18OjyabQxRXlC6shvRTqTDCpt1MPlfBWwyR2BKO3dHzk7h8T5=w1600-h766","https://lh3.googleusercontent.com/lqd5x1eNHsfzWpPeHNPe4u-ycQh1LyxWLp_mXi8tLvQGh4aNCbANfSfSWQdqhQy7c2J2V3a4dGIw6tRcMJCpFvsRrLLpXcFgHIjWpCWoxtgWC--0tMjb6W-YYKJX55zIhS1omxmSGPuQx1sZtsAL-XnRiqXbEIjGX1A_vbDObqVEc8TP3nVsraN5xLtektJbccNriwqqZ2CqpiuHagXKCRt3oa7D8N2ZygR-i04o8YP2pHr6I0Z76R6lZj1HDY65Sj-mkPJpN6nWKY-V_6htmMndJRY615MHntdsfZ82k5_IBbJXxdIN5MjJvgk41eyFXxzTKIXSGms-itEbW7FqMlZT8bIAigDoXYub9rh-FjtfdmVRVdwIIngzFzJrJQBroyHPxW9kW2JjH8foZCzX5YMStsHvfm1s4uAhZtbwK4KI_-x9GuXI3-cCUmtuFdQ-E2z_l3Hom57dasvYj6tFcqhRS9X_popdYTxR-4IeSE-NAjp71LDevvejtAqQTvpIRMFhV9um8qOb-xkPRe0xSoR6-chA2cQE--cbFJiLxe6ywBIqW6lI-aSI9Kv924s-OfRUGz0u=w1600-h766"];

- var text = {Forest: '“And into the forest I go, to lose my mind and find my soul”', Lake: '“Mist to mist, drops to drops. For water thou art, and unto water shalt thou return”', Cliffs: '“Go to the edge of the cliff and jump off. Build your wings on the way down”', Mountains: '“What are men to rocks and mountains?”', Peaks: '“On all the peaks lies peace”'};

#slider.slider(style="--img-prev:url(" + images[0] + ");")  
  #slider-content.slider__content
    .slider__images
      each val, i in images
        - var imgClassName = 'slider__images-item';
        if i+1 === 1
          - imgClassName += ' slider__images-item--active';
        div(class=imgClassName data-id=i+1)
          img(src=val)
        
    .slider__text
      - var i = 0;
      each val, key in text
        
        - var textClassName = 'slider__text-item';
        if ++i === 1
          - textClassName += ' slider__text-item--active';
        div(class=textClassName data-id=i)
          .slider__text-item-head
            h3= key
          .slider__text-item-info
            p= val
        
  .slider__nav
    .slider__nav-arrows
      #left.slider__nav-arrow.slider__nav-arrow--left to left
      #right.slider__nav-arrow.slider__nav-arrow--right to right
    #slider-dots.slider__nav-dots
      
      - var i = 0;
      while i++ < images.length
        - var dotsClassName = 'slider__nav-dot';
        if i === 1
          - dotsClassName += ' slider__nav-dot--active';
      
        div(class=dotsClassName data-id=i)
    
View Compiled
/*
  Note: the original SCSS code below was commented out due to some bug in
  Codepen's SCSS parser (the code itself is perfectly valid), so I temporarily
  pasted the compiled CSS for the demo to work.
*/

/*
@import url('https://fonts.googleapis.com/css?family=Lora:700');
@import url('https://fonts.googleapis.com/css?family=Open+Sans');

$item-width: 65vw;
$transition-time: .7s;
$transition-text-time: $transition-time / 2;
$offset: 1em;
$mobile-bkp: 650px;

:root {
  --z-distance: $item-width / 7.63;
  --from-left: 1;
  --mobile-bkp: $mobile-bkp;
}

*, *::before, *::after {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  margin: 0;
  padding: 0;
  overflow: hidden;
  font-family: Lora, serif;
  font-size: calc(14px + .3vw);
}

.slider {
  width: 100vw;
  height: 100vh;
  display: flex;
  perspective: 1000px;
  transform-style: preserve-3d;

  &::before, &::after {
    content: '';
    left: -1vw;
    top: -1vh;
    display: block;
    position: absolute;
    width: 102vw;
    height: 102vh;
    background-position: center;
    background-size: cover;
    will-change: opacity;
    // filter: blur(.2em);
    z-index: -1;
    box-shadow: 0 0 0 50vmax hsla(0, 50%, 0, .7) inset;
  }

  &::before {
    background-image: var(--img-prev);
  }
  &::after {
    transition: opacity $transition-time;
    opacity: 0;
    background-image: var(--img-next);
  }

  &--bg-next::after {
    opacity: 1;
  }

  &__content {
    margin: auto;
    width: $item-width;
    height: $item-width / 2;
    max-height: 60vh;
    will-change: transform;
    transform-style: preserve-3d;
    pointer-events: none;
    transform: translateZ(var(--z-distance));
  }
  &__images {
    overflow: hidden;
    position: absolute;
    width: 100%;
    height: 100%;
    z-index: 0;
    box-shadow: 0 0 5em #000;

    &-item {
      position: absolute;
      top: 0;
      left: 0;
      height: 100%;
      width: 100%;
      will-change: transform;
      transition-timing-function: ease-in;
      visibility: hidden;

      img {
        display: block;
        position: relative;
        left: -$offset;
        top: -$offset;
        width: calc(100% + #{$offset} * 2);
        height: calc(100% + #{$offset} * 2);
        object-fit: cover;
        will-change: transform;
      }
    }

    &-item--active {
      z-index: 20;
      visibility: visible;
    }

    &-item--subactive {
      z-index: 15;
      visibility: visible;
    }

    &-item--next {
      transform: translateX(100%);
    }

    &-item--prev {
      transform: translateX(-100%);
    }

    &-item--transit {
      transition: transform $transition-time, opacity $transition-time;
    }
  }
  &__text {
    position: relative;
    height: 100%;

    &-item {
      position: absolute;
      width: 100%;
      height: 100%;
      padding: 0.5em;
      perspective: 1000px;
      transform-style: preserve-3d;

      > * {
        overflow: hidden;
        position: absolute;
      }

      h3, & p {
        
        transition: transform $transition-text-time ease-out;
        line-height: 1.5;
        overflow: hidden;
      }

      h3 {
        background-color: hsla(0, 50%, 100%, 0.5);
      }

      p {
        font-family: 'Open Sans', sans-serif;
        padding: 1em;
        color: white;
        text-align: center;
        background-color: hsla(0, 0%, 0%, 0.5);
      }

      h3::before, & p::before {
        content: '';
        position: absolute;
        top: 0;
        left: 0;
        width: 105%;
        height: 100%;
        transform: translateX(0);
        transition: transform
          $transition-text-time
          ease-out
          $transition-text-time * .8;
      }

      h3::before {
        background-color: #000;
      }

      p::before {
        background-color: #fff;
      }

      h3 {
        margin: 0;
        font-size: 3.5em;
        padding: 0 .3em;
        position: relative;
        font-weight: 700;
        transform: translateX(-100%);
      }

      p {
        margin: 0;
        transform: translateX(100%);
      }
    }

    &-item-head {
      top: -0.5em;
      transform: translateZ(3em);
      clip-path: polygon(0 0, .5em 100%, 100% 100%, calc(100% - .3em) .3em);
    }

    &-item-info {
      bottom: 0;
      right: 0;
      max-width: 75%;
      min-width: min-content;
      transform: translateZ(2em);
      clip-path: polygon(0.5em 0, 100% 0%, calc(100% - .5em) 100%, 0 calc(100% - .5em));
    }

    &-item--active {
      h3, & p {
        transform: translateX(0);
      }

      h3::before {
        transform: translateX(100%);
      }
      p::before {
        transform: translateX(-100%);
      }
    }
    
    &-item--backwards {
      h3::before, p::before {
         transition: transform $transition-text-time ease-in;
      }
      h3, p {
        transition: transform $transition-text-time ease-in $transition-text-time;
      }
    }
  }

  &__nav {
    position: absolute;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    text-align: center;

    $arrow-size: 5vw;

    &-arrows {
      display: flex;
      justify-content: space-between;
      width: 100%;
      position: absolute;
      top: 0;
      left: 0;
    }

    &-arrow {
      height: 100vh;
      width: 50vw;
      text-indent: -9999px;
      white-space: nowrap;
 
      &--left {
        --arrow: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='80' height='80' viewBox='0 0 4 4'%3E %3Cpolyline points='3 1 1 2 3 3' stroke='white' stroke-width='.3' stroke-opacity='.5' fill='none'%3E%3C/polyline%3E %3C/svg%3E");
        cursor: var(--arrow) 40 40, auto;
      }

      &--right {
        --arrow: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='80' height='80' viewBox='0 0 4 4'%3E %3Cpolyline points='1 1 3 2 1 3' stroke='white' stroke-width='.3' stroke-opacity='.5' fill='none'%3E%3C/polyline%3E %3C/svg%3E");
        cursor: var(--arrow) 40 40, auto;
      }
    }
    
    $dot-clr: hsla(0, 50%, 100%, .5);
    $dot-size: 1em;
    $dot-border: 2px;
    
    &-dots {
      
      $pad: 1em;
      
      margin-top: 88vh;
      display: inline-flex;
      position: relative;
      padding: $pad;
      pointer-events: none;
      
      &::before {
        content: '';
        position: absolute;
        left: calc(#{$pad} + #{$dot-size} + #{$dot-border});
        top: calc(#{$pad} + #{$dot-border});
        width: calc(#{$dot-size} - #{$dot-border} * 2);
        height: calc(#{$dot-size} / 2 - #{$dot-border} * 2);
        background-color: hsla(0, 50%, 100%, .9);
        transition: transform $transition-time ease-out;
      transform: translateX(calc((#{$dot-size} + #{$pad} * 2) * (var(--from-left) - 1)));
      }
    }

    &-dot {
      margin: 0 $dot-size;
      width: $dot-size;
      height: $dot-size / 2;
      border: $dot-border solid $dot-clr;
      
       // The cursor is not the default one because of a weird bug 
       // related to custom cursors above
      
      cursor: crosshair;
      pointer-events: all;
      display: inline-block;
      
      &:hover {
        border-color: hsla(0, 50%, 100%, .7);
      }
      
      &:active {
        border-color: $dot-clr;
      }
    }
  }
}

@media only screen and (max-width: $mobile-bkp) {
  .slider::before,
  .slider::after {
      display: none;
  }
  .slider__content {
    width: 100vw;
    height: 100vh;
    max-height: 100vh;
  }
  .slider__text-item-info {
    bottom: 50%;
    left: 50%;
    transform: translate(-50%, 50%);
    
    p {
      padding: 1em .8em;
    }
  }
  .slider__text-item-head {
    top: 5vh;
    left: 10vw;
    transform: translateZ(0);
    h3 {
      font-size: 2.5em;
    }
  }
  .slider__nav-dots {
    background-color: hsla(0,50%,0%,.3);
  }
  .slider__nav-arrow {
    width: 10vw;
    position: relative;
    cursor: auto;
    
    &:active {
      filter: brightness(.5);
    }
    
    &::before {
      content: '';
      background-image: var(--arrow);
      background-size: cover;
      width: 8vw;
      height: 8vw;
      position: absolute;
      top: 50%;
      left: 50%;
      transform: translate(-50%, -50%);
    }
    &--left {
      background-image: linear-gradient(to right, hsla(0,50%,0%,.7) 0, transparent 100%);
      &:active {
        background-image: linear-gradient(to right, hsla(0,50%,0%,.9) 0, transparent 100%);
      }
    }
    &--right {
      background-image: linear-gradient(to left, hsla(0,50%,0%,.7) 0, transparent 100%);
      &:active {
        background-image: linear-gradient(to left, hsla(0,50%,0%,.9) 0, transparent 100%);
      }
    }
  }
}
*/

@import url("https://fonts.googleapis.com/css?family=Lora:700");
@import url("https://fonts.googleapis.com/css?family=Open+Sans");
:root {
  --z-distance: 8.519vw;
  --from-left: 1;
  --mobile-bkp: 650px;
}

*, *::before, *::after {
  box-sizing: border-box;
}

body {
  min-height: 100vh;
  margin: 0;
  padding: 0;
  overflow: hidden;
  font-family: Lora, serif;
  font-size: calc(14px + .3vw);
}

.slider {
  width: 100vw;
  height: 100vh;
  display: flex;
  perspective: 1000px;
  transform-style: preserve-3d;
}
.slider::before, .slider::after {
  content: '';
  left: -1vw;
  top: -1vh;
  display: block;
  position: absolute;
  width: 102vw;
  height: 102vh;
  background-position: center;
  background-size: cover;
  will-change: opacity;
  z-index: -1;
  box-shadow: 0 0 0 50vmax rgba(0, 0, 0, 0.7) inset;
}
.slider::before {
  background-image: var(--img-prev);
}
.slider::after {
  transition: opacity 0.7s;
  opacity: 0;
  background-image: var(--img-next);
}
.slider--bg-next::after {
  opacity: 1;
}
.slider__content {
  margin: auto;
  width: 65vw;
  height: 32.5vw;
  max-height: 60vh;
  will-change: transform;
  transform-style: preserve-3d;
  pointer-events: none;
  transform: translateZ(var(--z-distance));
}
.slider__images {
  overflow: hidden;
  position: absolute;
  width: 100%;
  height: 100%;
  z-index: 0;
  box-shadow: 0 0 5em #000;
}
.slider__images-item {
  position: absolute;
  top: 0;
  left: 0;
  height: 100%;
  width: 100%;
  will-change: transform;
  transition-timing-function: ease-in;
  visibility: hidden;
}
.slider__images-item img {
  display: block;
  position: relative;
  left: -1em;
  top: -1em;
  width: calc(100% + 1em * 2);
  height: calc(100% + 1em * 2);
  object-fit: cover;
  will-change: transform;
}
.slider__images-item--active {
  z-index: 20;
  visibility: visible;
}
.slider__images-item--subactive {
  z-index: 15;
  visibility: visible;
}
.slider__images-item--next {
  transform: translateX(100%);
}
.slider__images-item--prev {
  transform: translateX(-100%);
}
.slider__images-item--transit {
  transition: transform 0.7s, opacity 0.7s;
}
.slider__text {
  position: relative;
  height: 100%;
}
.slider__text-item {
  position: absolute;
  width: 100%;
  height: 100%;
  padding: 0.5em;
  perspective: 1000px;
  transform-style: preserve-3d;
}
.slider__text-item > * {
  overflow: hidden;
  position: absolute;
}
.slider__text-item h3, .slider__text-item p {
  transition: transform 0.35s ease-out;
  line-height: 1.5;
  overflow: hidden;
}
.slider__text-item h3 {
  background-color: rgba(255, 255, 255, 0.5);
}
.slider__text-item p {
  font-family: 'Open Sans', sans-serif;
  padding: 1em;
  color: white;
  text-align: center;
  background-color: rgba(0, 0, 0, 0.5);
}
.slider__text-item h3::before, .slider__text-item p::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  width: 105%;
  height: 100%;
  transform: translateX(0);
  transition: transform 0.35s ease-out 0.28s;
}
.slider__text-item h3::before {
  background-color: #000;
}
.slider__text-item p::before {
  background-color: #fff;
}
.slider__text-item h3 {
  margin: 0;
  font-size: 3.5em;
  padding: 0 .3em;
  position: relative;
  font-weight: 700;
  transform: translateX(-100%);
}
.slider__text-item p {
  margin: 0;
  transform: translateX(100%);
}
.slider__text-item-head {
  top: -0.5em;
  transform: translateZ(3em);
}
.slider__text-item-info {
  bottom: 0;
  right: 0;
  max-width: 75%;
  min-width: min-content;
  transform: translateZ(2em);
}
.slider__text-item--active h3, .slider__text-item--active p {
  transform: translateX(0);
}
.slider__text-item--active h3::before {
  transform: translateX(102%);
}
.slider__text-item--active p::before {
  transform: translateX(-102%);
}
.slider__text-item--backwards h3::before, .slider__text-item--backwards p::before {
  transition: transform 0.35s ease-in;
}
.slider__text-item--backwards h3, .slider__text-item--backwards p {
  transition: transform 0.35s ease-in 0.35s;
}
.slider__nav {
  position: absolute;
  left: 0;
  top: 0;
  width: 100%;
  height: 100%;
  text-align: center;
}
.slider__nav-arrows {
  display: flex;
  justify-content: space-between;
  width: 100%;
  position: absolute;
  top: 0;
  left: 0;
}
.slider__nav-arrow {
  height: 100vh;
  width: 50vw;
  text-indent: -9999px;
  white-space: nowrap;
}
.slider__nav-arrow--left {
  --arrow: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='80' height='80' viewBox='0 0 4 4'%3E %3Cpolyline points='3 1 1 2 3 3' stroke='white' stroke-width='.3' stroke-opacity='.5' fill='none'%3E%3C/polyline%3E %3C/svg%3E");
  cursor: var(--arrow) 40 40, auto;
}
.slider__nav-arrow--right {
  --arrow: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='80' height='80' viewBox='0 0 4 4'%3E %3Cpolyline points='1 1 3 2 1 3' stroke='white' stroke-width='.3' stroke-opacity='.5' fill='none'%3E%3C/polyline%3E %3C/svg%3E");
  cursor: var(--arrow) 40 40, auto;
}
.slider__nav-dots {
  margin-top: 88vh;
  display: inline-flex;
  position: relative;
  padding: 1em;
  pointer-events: none;
}
.slider__nav-dots::before {
  content: '';
  position: absolute;
  left: calc(1em + 1em + 2px);
  top: calc(1em + 2px);
  width: calc(1em - 2px * 2);
  height: calc(1em / 2 - 2px * 2);
  background-color: rgba(255, 255, 255, 0.9);
  transition: transform 0.7s ease-out;
  transform: translateX(calc((1em + 1em * 2) * (var(--from-left) - 1)));
}
.slider__nav-dot {
  margin: 0 1em;
  width: 1em;
  height: 0.5em;
  border: 2px solid rgba(255, 255, 255, 0.5);
  cursor: crosshair;
  pointer-events: all;
  display: inline-block;
}
.slider__nav-dot:hover {
  border-color: rgba(255, 255, 255, 0.7);
}
.slider__nav-dot:active {
  border-color: rgba(255, 255, 255, 0.5);
}

@media only screen and (max-width: 650px) {
  .slider::before,
  .slider::after {
    display: none;
  }

  .slider__content {
    width: 100vw;
    height: 100vh;
    max-height: 100vh;
  }

  .slider__text-item-info {
    bottom: 50%;
    left: 50%;
    transform: translate(-50%, 50%);
  }
  .slider__text-item-info p {
    padding: 1em .8em;
  }

  .slider__text-item-head {
    top: 5vh;
    left: 10vw;
    transform: translateZ(0);
  }
  .slider__text-item-head h3 {
    font-size: 2.5em;
  }

  .slider__nav-dots {
    background-color: rgba(0, 0, 0, 0.3);
  }

  .slider__nav-arrow {
    width: 10vw;
    position: relative;
    cursor: auto;
  }
  .slider__nav-arrow:active {
    filter: brightness(0.5);
  }
  .slider__nav-arrow::before {
    content: '';
    background-image: var(--arrow);
    background-size: cover;
    width: 8vw;
    height: 8vw;
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
  }
  .slider__nav-arrow--left {
    background-image: linear-gradient(to right, rgba(0, 0, 0, 0.7) 0, transparent 100%);
  }
  .slider__nav-arrow--left:active {
    background-image: linear-gradient(to right, rgba(0, 0, 0, 0.9) 0, transparent 100%);
  }
  .slider__nav-arrow--right {
    background-image: linear-gradient(to left, rgba(0, 0, 0, 0.7) 0, transparent 100%);
  }
  .slider__nav-arrow--right:active {
    background-image: linear-gradient(to left, rgba(0, 0, 0, 0.9) 0, transparent 100%);
  }
}
/*
  More about this function - 
  https://codepen.io/rachsmith/post/animation-tip-lerp
*/
function lerp({ x, y }, { x: targetX, y: targetY }) {
  const fraction = 0.1;
  
  x += (targetX - x) * fraction;
  y += (targetY - y) * fraction;
  
  return { x, y };
}

class Slider {
  constructor (el) {
    const imgClass = this.IMG_CLASS = 'slider__images-item';
    const textClass = this.TEXT_CLASS = 'slider__text-item';
    const activeImgClass = this.ACTIVE_IMG_CLASS = `${imgClass}--active`;
    const activeTextClass = this.ACTIVE_TEXT_CLASS =  `${textClass}--active`;
    
    this.el = el;
    this.contentEl = document.getElementById('slider-content');
    this.onMouseMove = this.onMouseMove.bind(this);
    
    // taking advantage of the live nature of 'getElement...' methods
    this.activeImg = el.getElementsByClassName(activeImgClass);
    this.activeText = el.getElementsByClassName(activeTextClass);
    this.images = el.getElementsByTagName('img');
    
    document.getElementById('slider-dots')
      .addEventListener('click', this.onDotClick.bind(this));
    
    document.getElementById('left')
      .addEventListener('click', this.prev.bind(this));
    
    document.getElementById('right')
      .addEventListener('click', this.next.bind(this));
    
    window.addEventListener('resize', this.onResize.bind(this));
    
    this.onResize();
    
    this.length = this.images.length;
    this.lastX = this.lastY = this.targetX = this.targetY = 0;
  }
  onResize () {
    const htmlStyles = getComputedStyle(document.documentElement);
    const mobileBreakpoint =  htmlStyles.getPropertyValue('--mobile-bkp');
    
    const isMobile = this.isMobile = matchMedia(
      `only screen and (max-width: ${mobileBreakpoint})`
    ).matches;
    
    this.halfWidth = innerWidth / 2;
    this.halfHeight = innerHeight / 2;
    this.zDistance = htmlStyles.getPropertyValue('--z-distance');
    
    if (!isMobile && !this.mouseWatched) {
      this.mouseWatched = true;
      this.el.addEventListener('mousemove', this.onMouseMove);
      this.el.style.setProperty(
        '--img-prev', 
        `url(${this.images[+this.activeImg[0].dataset.id - 1].src})`
      );
      this.contentEl.style.setProperty('transform', `translateZ(${this.zDistance})`);
    } else if (isMobile && this.mouseWatched) {
      this.mouseWatched = false;
      this.el.removeEventListener('mousemove', this.onMouseMove);
      this.contentEl.style.setProperty('transform', 'none');
    }
  }
  getMouseCoefficients ({ pageX, pageY } = {}) {
    const halfWidth = this.halfWidth;
    const halfHeight = this.halfHeight;
    const xCoeff = ((pageX || this.targetX) - halfWidth) / halfWidth;
    const yCoeff = (halfHeight - (pageY || this.targetY)) / halfHeight;
    
    return { xCoeff,  yCoeff }
  }
  onMouseMove ({ pageX, pageY }) {   
    this.targetX = pageX;
    this.targetY = pageY;
    
    if (!this.animationRunning) {
      this.animationRunning = true;
      this.runAnimation();
    }
  }
  runAnimation () {
    if (this.animationStopped) {
      this.animationRunning = false;
      return;
    }
    
    const maxX = 10;
    const maxY = 10;
    
    const newPos = lerp({
      x: this.lastX,
      y: this.lastY
    }, {
      x: this.targetX,
      y: this.targetY
    });
    
    const { xCoeff, yCoeff } = this.getMouseCoefficients({
      pageX: newPos.x, 
      pageY: newPos.y
    });
      
    this.lastX = newPos.x;
    this.lastY = newPos.y;

    this.positionImage({ xCoeff, yCoeff });
    
    this.contentEl.style.setProperty('transform', `
      translateZ(${this.zDistance})
      rotateX(${maxY * yCoeff}deg)
      rotateY(${maxX * xCoeff}deg)
    `);
    
    if (this.reachedFinalPoint) {
      this.animationRunning = false;
    } else {
      requestAnimationFrame(this.runAnimation.bind(this)); 
    }
  }
  get reachedFinalPoint () {
    const lastX = ~~this.lastX;
    const lastY = ~~this.lastY;
    const targetX = this.targetX;
    const targetY = this.targetY;
    
    return (lastX == targetX || lastX - 1 == targetX || lastX + 1 == targetX) 
        && (lastY == targetY || lastY - 1 == targetY || lastY + 1 == targetY);
  }
  positionImage ({ xCoeff, yCoeff }) {
    const maxImgOffset = 1;
    const currentImage = this.activeImg[0].children[0];
    
    currentImage.style.setProperty('transform', `
      translateX(${maxImgOffset * -xCoeff}em)
      translateY(${maxImgOffset * yCoeff}em)
    `);  
  }
  onDotClick ({ target }) {
    if (this.inTransit) return;
    
    const dot = target.closest('.slider__nav-dot');
    
    if (!dot) return;
    
    const nextId = dot.dataset.id;
    const currentId = this.activeImg[0].dataset.id;
    
    if (currentId == nextId) return;
    
    this.startTransition(nextId);
  }
  transitionItem (nextId) {
    function onImageTransitionEnd (e) {
      e.stopPropagation();
      
      nextImg.classList.remove(transitClass);
      
      self.inTransit = false;
      
      this.className = imgClass;
      this.removeEventListener('transitionend', onImageTransitionEnd);
    }
    
    const self = this;
    const el = this.el;
    const currentImg = this.activeImg[0];
    const currentId = currentImg.dataset.id;
    const imgClass = this.IMG_CLASS;
    const textClass = this.TEXT_CLASS;
    const activeImgClass = this.ACTIVE_IMG_CLASS;
    const activeTextClass = this.ACTIVE_TEXT_CLASS;
    const subActiveClass = `${imgClass}--subactive`;
    const transitClass = `${imgClass}--transit`;
    const nextImg = el.querySelector(`.${imgClass}[data-id='${nextId}']`);
    const nextText = el.querySelector(`.${textClass}[data-id='${nextId}']`);
    
    let outClass = '';
    let inClass = '';

    this.animationStopped = true;
    
    nextText.classList.add(activeTextClass);
    
    el.style.setProperty('--from-left', nextId);
    
    currentImg.classList.remove(activeImgClass);
    currentImg.classList.add(subActiveClass);
    
    if (currentId < nextId) {
      outClass = `${imgClass}--next`;
      inClass = `${imgClass}--prev`;
    } else {
      outClass = `${imgClass}--prev`;
      inClass = `${imgClass}--next`;
    }
    
    nextImg.classList.add(outClass);
    
    requestAnimationFrame(() => {
      nextImg.classList.add(transitClass, activeImgClass);
      nextImg.classList.remove(outClass);
      
      this.animationStopped = false;
      this.positionImage(this.getMouseCoefficients());
      
      currentImg.classList.add(transitClass, inClass);
      currentImg.addEventListener('transitionend', onImageTransitionEnd);
    });

    if (!this.isMobile)
      this.switchBackgroundImage(nextId);
  }
  startTransition (nextId) {
    function onTextTransitionEnd(e) {
      if (!e.pseudoElement) {
        e.stopPropagation();

        requestAnimationFrame(() => {
          self.transitionItem(nextId);
        });

        this.removeEventListener('transitionend', onTextTransitionEnd);
      }
    }
    
    if (this.inTransit) return;

    const activeText = this.activeText[0];
    const backwardsClass = `${this.TEXT_CLASS}--backwards`;
    const self = this;
    
    this.inTransit = true;
    
    activeText.classList.add(backwardsClass);
    activeText.classList.remove(this.ACTIVE_TEXT_CLASS);
    activeText.addEventListener('transitionend', onTextTransitionEnd);
    
    requestAnimationFrame(() => {
      activeText.classList.remove(backwardsClass);
    });
  }
  next () {
    if (this.inTransit) return;
    
    let nextId = +this.activeImg[0].dataset.id + 1;
    
    if (nextId > this.length)
        nextId = 1;
    
    this.startTransition(nextId);
  }
  prev () {
    if (this.inTransit) return;
    
    let nextId = +this.activeImg[0].dataset.id - 1;
    
    if (nextId < 1)
        nextId = this.length;
    
    this.startTransition(nextId);
  }
  switchBackgroundImage (nextId) {
    function onBackgroundTransitionEnd (e) {
      if (e.target === this) {
        this.style.setProperty('--img-prev', imageUrl);
        this.classList.remove(bgClass);
        this.removeEventListener('transitionend', onBackgroundTransitionEnd);
      }
    }

    const bgClass = 'slider--bg-next';
    const el = this.el;
    const imageUrl = `url(${this.images[+nextId - 1].src})`;
    
    el.style.setProperty('--img-next', imageUrl);
    el.addEventListener('transitionend', onBackgroundTransitionEnd);
    el.classList.add(bgClass);
  }
}

const sliderEl = document.getElementById('slider');
const slider = new Slider(sliderEl);

// ------------------ Demo stuff ------------------------ //

let timer = 0;

function autoSlide () {
  requestAnimationFrame(() => {
    slider.next();
  });
  
  timer = setTimeout(autoSlide, 5000);
}

function stopAutoSlide () {
  clearTimeout(timer);
  
  this.removeEventListener('touchstart', stopAutoSlide);
  this.removeEventListener('mousemove', stopAutoSlide);  
}

sliderEl.addEventListener('mousemove', stopAutoSlide);
sliderEl.addEventListener('touchstart', stopAutoSlide);

timer = setTimeout(autoSlide, 2000);
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