*, *:before, *:after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
html, body {
  font-size: 62.5%;
  height: 100%;
  overflow: hidden;
}

$openSans: 'Open Sans', Helvetica, Arial, sans-serif;
$bg1: 'http://i.imgur.com/653n5b8.jpg';
$bg2: 'http://i.imgur.com/sgd4qub.jpg';
$bg3: 'http://i.imgur.com/j9u7AY4.jpg';
$bg4: 'http://i.imgur.com/KruZmzA.jpg';
$bg5: 'http://i.imgur.com/3pu2X8D.jpg';
$elN: 4;
$timeoutDelay: 2s;
$timeoutTime: 6s;

.instant {
  transition: 0 0 !important;
}

.scene {
  position: relative;
  height: 100%;
  background: #fff;
  transition: transform 0.5s;
  will-change: transform;
  
  &.menu-visible {
    
    .menu__btn {
      background: #000;
      color: #000;
      
      &:after {
        transform: scale(1.5) !important;
      }
    }
    
    .menu__heading {
      opacity: 1;
      transition: opacity 0.5s 1.7s;
    }
  }
}

.content {
  position: relative;
  height: 100%;
  transition: transform 0.6s, opacity 0.4s 0.1s;
  will-change: transform, opacity;
  
  &.inactive {
    opacity: 0;
    transform: scale(0.9);
  }
}

.back,
.front {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  transition: transform 0.5s 0.5s;
  will-change: transform;

  &__bg {
    position: absolute;
    left: 0;
    width: 100%;
    height: 100%;
    background-size: cover;
    transition: transform 0.5s;
    will-change: transform;

    &-1 {
      background-image: url(#{$bg1});
    }
    &-2 {
      background-image: url(#{$bg2});
    }
    &-3 {
      background-image: url(#{$bg3});
    }
    &-4 {
      background-image: url(#{$bg4});
    }
  }
}

.back__bg {
  
  &.hidden {
    display: none;
  }

  &:after {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.5);
  }
  
  @for $i from 1 through $elN {
    &-#{$i} {
      top: ($i - 1) * 100%;
    }
  }
}

.front__bg {
  transform: scale(0.8);
  
  &.active {
    transform: scale(1);
  }
  
  &:after {
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0,0,0,0.25);
  }
  
  @for $i from 0 through $elN {
    &-#{$i} {
      top: ($i - 1) * -100%;
    }
  }
}

.nav {
  position: absolute;
  left: 0;
  bottom: 20%;
  width: 100%;
  text-align: center;
  
  &__el {
    display: inline-block;
    position: relative;
    font-size: 2.5rem;
    height: 3.5rem;
    text-transform: uppercase;
    color: rgba(255,255,255,.5);
    font-family: $openSans;
    margin: 1rem 2rem;
    padding-left: 1.5rem;
    cursor: pointer;
    overflow: hidden;
    
    &-clone {
      position: absolute;
      top: 0;
      left: 0;
      overflow: hidden;
      transition: transform 0.5s;
      will-change: transform;
      transform: translateX(-100%);
      
      > div {
        margin: 0;
        color: #fff;
        transition: transform 0.5s;
        will-change: transform;
        transform: translateX(100%);
      }
    }
    
    &.active {
      
      &:after {
        transform: scale(1);
      }
      
      .nav__el-clone {
        transform: scale(1);
        transition: transform $timeoutTime $timeoutDelay;

        .nav__el {
          transform: scale(1);
          transition: transform $timeoutTime $timeoutDelay;
        }
      }
    }
    
    &:before {
      position: absolute;
      top: 50%;
      margin-top: -1rem;
      left: -0.3rem;
      font-size: 1.5rem;
      transform: rotate(-90deg);
    }
    
    &:after {
      content: "";
      position: absolute;
      left: 0;
      bottom: 0;
      width: 100%;
      height: 1px;
      background: #fff;
      transition: transform 1.5s;
      transform: scale(0);
    }
    
    @for $i from 1 through $elN {
      &-#{$i}:before {
        content: "0" + $i;
      }
    }
  }
}

.menu {
  
  &__btn {
    z-index: 5;
    position: absolute;
    top: 5%;
    right: 5%;
    width: 5.2rem;
    height: 5.2rem;
    border: 2px solid;
    color: #fff;
    overflow: hidden;
    cursor: pointer;
    transition: background-color 0.5s;
    
    &:hover {
      
      &:after {
        transform: scale(1);
      }
      
      .menu__btn-line {
        @for $i from 1 through 3 {
          &:nth-child(#{$i}) {
            animation: animateMenuBtn 0.7s ($i - 1)*0.2s;
          }
        }
      }
    }
    
    &:after {
      content: "";
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      border: 0.5rem solid #fff;
      transition: transform 0.6s;
      will-change: transform;
      transform: scale(1.5);
    }
    
    &-inner {
      position: absolute;
      top: 1.6rem;
      left: 1.2rem;
      width: 2.4rem;
      height: 1.6rem;
      overflow: hidden;
    }
    
    &-line {
      position: absolute;
      left: 0;
      width: 100%;
      height: 2px;
      background: #fff;
      
      &:nth-child(1) {
        top: 0;
      }
      &:nth-child(2) {
        top: 0.7rem;
      }
      &:nth-child(3) {
        top: 1.4rem;
      }
    }
  }

  &__block {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: none;
    text-align: center;
    
    &.visible {
      display: block;
    }
    
    &-bg {
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      background-size: cover;
      background-image: url(#{$bg5});
    }
    
    &-svg {
      overflow: visible;
      display: block;
      position: absolute;
      top: 0;
      left: 0;
      width: 100%;
      height: 100%;
      
      &Path {
        fill: #fff;
      }
    }
  }

  &__heading {
    position: absolute;
    max-width: 60rem;
    top: 50%;
    left: 50%;
    transform: translateX(-50%) translateY(-50%);
    font-size: 4rem;
    color: #000;
    text-transform: uppercase;
    opacity: 0;
    transition: opacity 0.3s;
    text-align: center;
  }
}

@keyframes animateMenuBtn {
  49.9% {
    transform: translateX(100%);
  }
  50% {
    transform: translateX(-100%);
  }
  100% {
    transform: translateX(0);
  }
}