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HTML

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CSS

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CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

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JavaScript

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JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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HTML 

              
                input(type="checkbox")#check
label(for="check").switch
label(for="check").on ON
label(for="check").off OFF
!

CSS 

              
                @import "bourbon";

@import url(https://fonts.googleapis.com/css?family=Raleway:300,400);

$switch-size: 50px;
$edges: 50%;
$push: 180px;

$bgc: #905468;
$accent: #C2DFE3;
$off: #7D3238;
$on: #3bb143;
$none: #777;

$spacing: 5px;
$touch: 5px;

html,
body {
  position: relative;
  width: 100%;
  height: 100%;
}

body {
  background-color: $bgc;
  background-image: url(https://i.imgur.com/HWVPDtP.jpg);
  background-position: center center;
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
  
  overflow: hidden;
  
  font-family: 'Raleway';
  
  @include perspective(500px);
}

#check {
  display: none;
  
  &:checked ~ .switch {
    background-color: #3bb143;
    @include transform(rotate(135deg));
  }
  
  &:checked ~ .on {
    opacity: 1;
    @include animation(0.5s spring);
    @include animation-delay(0.25s);
    color: $on;
  }
  
  &:checked ~ .off {
    color: $none;
  }
  
  &:not(:checked) ~ .off {
    opacity: 1;
    @include animation(0.5s spring);
    @include animation-delay(0.25s);
    $color: $off;
  }
}

.switch {
  margin: auto;
  @include position(absolute, 0 0 0 0);
  @include box-sizing(border-box);
  
  width: $switch-size;
  height: $switch-size;
  
  background-color: $off;
  
  @include border-bottom-radius($edges);
  border-top-right-radius: $edges;
  
  border: 5px solid $accent;
  
  box-shadow: 0 0 8px 0 rgba(0, 0, 0, 0.25);
  
  @include transition(all 0.25s ease-in-out);
  @include transform(rotate(-45deg));
  // Possible alternative animation
  //@include transform(rotate(-135deg) rotateY(180deg));
  
  cursor: pointer;
}

.on,
.off {
  margin: auto;
  @include position(absolute, 0 0 0 0);
  width: 80px;
  height: 40px;
  
  opacity: 0.5;
  
  background-color: $accent;
  box-shadow: 0 0 8px 1px rgba(0, 0, 0, 0.25);
  
  font: {
    weight: 300;
    size: 1.1em;
  }
  text-indent: $spacing;
  letter-spacing: $spacing;
  line-height: 40px;
  text-align: center;
  color: $none;
  
  cursor: pointer;
  
  @include transition(all 0.25s ease-in-out);
}

.on {
  left: $push;
  @include border-right-radius($touch);
}

.off {
  right: $push;
  @include border-left-radius($touch);
  color: $off;
}

@include keyframes(spring) {
  50% {
    top: 10px;
  }
}

// 353535-ffffff-96b2c6-905468-7d3238
!

JS 

              
                // Little bit of switch state randomness, rest is pure CSS

;(function (window, document, undefined) {
  var check, RNG;

  check = document.getElementById('check');
  RNG = Math.round(Math.random());
  
  check.checked = !!RNG;
  
}(window, document));
!
999px

Console