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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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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <div class="clock">
  <div class="hour-marks">
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
    <div></div>
  </div>
  <div class="hands">
    <div class="hand hour no-transition"></div>
    <div class="hand minute no-transition"></div>
    <div class="hand second no-transition"></div>
  </div>
</div>
!

CSS 

              
                $color-dark-blue: #2c3e50;
$color-light-gray: #ecf0f1;
$color-yellow: #f1c40f;
$color-concrete: #95a5a6;
$color-red: #e74c3c;

$shadow-color: rgba(0, 0, 0, 0.03);

$clock-height: 70vh;
$clock-width: $clock-height;

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

body {
  display: flex;
  align-items: center;
  justify-content: center;
  background-color: $color-light-gray;
}

.clock {
  overflow: hidden;
  position: relative;
  width: $clock-width;
  height: $clock-height;
  background-color: $color-light-gray;
  border: 2vh solid $color-yellow;
  border-radius: 4vh;
  box-shadow: 
    1vh 1vh 0 $shadow-color,
    1.5vh 1.5vh 0 $shadow-color,
    2vh 2vh 0 $shadow-color, 
    2.5vh 2.5vh 0 $shadow-color, 
    3vh 3vh 0 $shadow-color, 
    3.5vh 3.5vh 0 $shadow-color, 
    4vh 4vh 0 $shadow-color, 
    5vh 5vh 0 $shadow-color, 
    6vh 6vh 0 $shadow-color,
    8vh 8vh 1vh $shadow-color,
    10vh 10vh 1vh $shadow-color,
    13vh 13vh 2vh $shadow-color,
    16vh 16vh 4vh $shadow-color,
    20vh 20vh 6vh $shadow-color,
    30vh 30vh 8vh $shadow-color,
    40vh 40vh 10vh $shadow-color;
  
  &:before {
    content: "";
    width: 150%;
    height: 150%;
    background-color: rgba(255, 255, 255, 0.7);
    position: absolute;
    border-radius: 0 0 100% 0;
    top: -40%;
    left: -40%;
  }
}

.hour-marks {
  width: 100%;
  height: 100%;
  position: relative;
  
  div {
    background-color: $color-concrete;
    width: 1vh;
    height: 7vh;
    position: absolute;
    transform-origin: $clock-width/2 $clock-width/2;
    
    @for $i from 1 through 12 {
      &:nth-child(#{$i}) {
        transform: rotateZ(30deg * $i) translate($clock-width/2 - 0.5, 2vh);
      }
    }
  }
}

.hands {
  position: absolute;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  
  .hand {
    position: absolute;
    
    &.no-transition {
      transition: none !important;
    }
    
    &.second {
      transition: transform 1s linear;
      width: 0.5vh;
      height: $clock-height/2;
      background-color: $color-red;
      left: $clock-height/2 - 0.25;
      top: 5vh;
      transform-origin: .25vh 30vh;
    }
    
    &.minute {
      transition: transform 0.2s ease-out;
      width: 1vh;
      height: $clock-height/2;
      background-color: $color-dark-blue;
      left: $clock-height/2 - 0.5;
      top: 5vh;
      transform-origin: 0.5vh 30vh;
    }
    
    &.hour {
      transition: transform 0.2s ease-out;
      width: 1vh;
      height: $clock-height/2 - 10vh;
      background-color: $color-dark-blue;
      left: $clock-height/2 - 0.5;
      top: 15vh;
      transform-origin: 0.5vh 20vh;
    }
  }
}
!

JS 

              
                const hands = {
  second: document.querySelector('.hand.second'),
  minute: document.querySelector('.hand.minute'),
  hour: document.querySelector('.hand.hour')
};

let prevTime = new Date();

const rotate = (el, deg) => {
  el.style.transform = `rotate(${deg}deg)`;
};

const resetCycle = el => {
  rotate(el, 360);
  setTimeout(() => {
    el.classList.add('no-transition');
    rotate(el, 0);
  },900);
}

const updateHand = (el, value, denominator) => {
  el.classList.remove('no-transition');
  if(value === 0) {
    resetCycle(el);
  }
  else {
    rotate(el, (360/denominator)*value);
  }
}

const updateSeconds = () => {
  const date = new Date();
  if(prevTime.getSeconds() !== date.getSeconds()) {
    updateHand(hands.second, date.getSeconds(), 60);
  }
};

const updateMinutes = () => {
  const date = new Date();
  if(prevTime.getMinutes() !== date.getMinutes()) {
    updateHand(hands.minute, date.getMinutes(), 60);
  }
};

const updateHours = () => {
  const date = new Date();
  if(prevTime.getHours() !== date.getHours()) {
    updateHand(hands.hour, date.getHours(), 12);
  }
};

const updateTime = () => {
  setTimeout(() => {
    const d = new Date();
    
    updateSeconds();
    updateMinutes();
    updateHours();
    
    prevTime = d;
    updateTime();
  }, 50);
};

// Set the hands initial rotation (without a transition)
rotate(hands.second, (360/60)*prevTime.getSeconds());
rotate(hands.minute, (360/60)*prevTime.getMinutes());
rotate(hands.hour, (360/12/60)*(prevTime.getHours()*60 + prevTime.getMinutes()));

// Begin updating the time
updateTime();
!
999px

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