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CSS

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HTML 

              
                <div class="toggle">

  <input type="checkbox" id="btn">
  <label for="btn">
    <span class="thumb"></span>
  </label>
  <div class="lights">
    <span class="light-off"></span>
    <span class="light-on"></span>
  </div>

</div>
!

CSS 

              
                /*** IN PROGRESS ***/
:root {
  --sz: 10vmin;
  --on: #99dc39;
  --of: #F44336;
  --lg: var(--of);
  --sp: 1s;
}	

*, *:before, *:after {
  box-sizing: border-box;
  transition: all var(--sp) ease 0s;
}

body {
  margin: 0;
  padding: 0;
  width: 100vw;
  height: 100vh;
  overflow: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: none;
  background: linear-gradient(135deg, #1f1f23, #2d2d31, #101012);
  background: linear-gradient(135deg, #161618, #212125, #060606);
  
}

body:before, body:after {
  content: "";
  position: absolute;
  width: 100%;
  height: 100%;
  background: 
    repeating-conic-gradient(#0002 0.000095%, #fff0 .0005%, #fff0 .005%, #fff0 .0005%), 
    repeating-conic-gradient(#0002 0.00001%, #fff0 .00009%, #fff0 .00075%, #fff0 .000025%);
  opacity: 0.75;
  filter: blur(0.75px);
}

.toggle {
  position: relative;
  width: calc(var(--sz) * 5.55);
  height: calc(var(--sz) * 2);
  display: flex;
  align-items: center;
  justify-content: center;
}

input {
  display: none;
}

label[for=btn] {
  position: absolute;
  width: calc(var(--sz) * 5.55);
  height: calc(var(--sz) * 2);
  background: linear-gradient(0deg, #12172080, #0d121780);
  border-radius: var(--sz);
  display: flex;
  align-items: center;
  /*
  box-shadow: 
  0 0 calc(var(--sz) / 50) calc(var(--sz) / 50) #0006, 
  0 calc(var(--sz) / -20) calc(var(--sz) / 5) calc(var(--sz) / 25) #0b0b10, 
  0 calc(var(--sz) / 20) calc(var(--sz) / 10) calc(var(--sz) / 50) #f5f5f588, 
  0 calc(var(--sz) / -20) calc(var(--sz) / 50) calc(var(--sz) / 15) #00000060;
  */
  background: radial-gradient(circle at 50% calc(var(--sz) / 0.085), #fff0 calc(var(--sz) / 0.1), #000 calc(calc(var(--sz) / 0.1) + 1px) calc(var(--sz) / 0.0875), #fff0 calc(calc(var(--sz) / 0.0875) + 1px) 100%), 
    radial-gradient(circle at 50% calc(var(--sz) / -0.1025), #fff0 calc(var(--sz) / 0.1), #000 calc(calc(var(--sz) / 0.1) + 1px) calc(var(--sz) / 0.0875), #fff0 calc(calc(var(--sz) / 0.0875) + 1px) 100%);
}

label[for=btn]:before {
  content: "";
  position: absolute;
  width: 100%;
  height: 100%;
  border-radius: var(--sz);
  /* box-shadow: 0 0 calc(var(--sz) / 3) calc(var(--sz) / 10) #000 inset; */
  background: radial-gradient(circle at 50% calc(var(--sz) / 0.0845), #fff0 calc(var(--sz) / 0.1), #121212 calc(calc(var(--sz) / 0.1) + 1px) calc(var(--sz) / 0.0875), #fff0 calc(calc(var(--sz) / 0.0875) + 1px) 100%), radial-gradient(circle at 50% calc(var(--sz) / -0.1015), #fff0 calc(var(--sz) / 0.1), #121212 calc(calc(var(--sz) / 0.1) + 1px) calc(var(--sz) / 0.0875), #fff0 calc(calc(var(--sz) / 0.0875) + 1px) 100%);
  filter: drop-shadow(0px -2px 1px #000) drop-shadow(0px -2px 2px #000) drop-shadow(0px -2px 3px #0008) drop-shadow(0px 2px 2px #fff8);
}

.thumb {
  position: absolute;
  width: calc(calc(var(--sz) * 2) - calc(var(--sz) / 8));
  height: calc(calc(var(--sz) * 2) - calc(var(--sz) / 8));
  margin-top: calc(calc( var(--sz) / 10) + calc(var(--sz) / -7));
  left: calc(calc( var(--sz) / 10) + calc(var(--sz) / -30));
  background: 

    /* radial-gradient( #fff0 0 calc(var(--sz) / 3.5), var(--lg) calc(calc(var(--sz) / 3) + 1px) calc(var(--sz) / 2.75), #fff0 calc(var(--sz) / 1.15)), */
    linear-gradient(0deg, #212121, #fff0 35% 65%, #474747), 
    radial-gradient( #fff0 0 calc(var(--sz) / 3), #393939 calc(calc(var(--sz) / 3) + 1px) calc(var(--sz) / 1), #474747);
  border-radius: var(--sz);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 1;
  overflow: hidden;
  box-shadow: 
    0 0 calc(var(--sz) / 3) calc(var(--sz) / -8) var(--lg), 
    0 0 calc(var(--sz) / 5) calc(var(--sz) / -15) var(--lg) inset, 
    calc(var(--sz) / -50) calc(var(--sz) / 50) calc(var(--sz) / 30) 0 #fff2 inset, 0 0 calc(var(--sz) / 10) calc(var(--sz) / 50) #000c, 0 calc(var(--sz) / 4) calc(var(--sz) / 5) 0 #000d;
  animation: grow calc(var(--sp) / 3) ease 0s 2 alternate;
}

#btn:checked + label .thumb {
  --lg: var(--on);
  left: calc(calc(100% - calc(calc(var(--sz) * 2) - calc(var(--sz) / 3))) - calc(calc( var(--sz) / 10) + calc(var(--sz) / 6)));
  /*
  box-shadow: 
  calc(var(--sz) / 10) 0 calc(var(--sz) / 10) calc(var(--sz) / -10) var(--lg), 
  calc(var(--sz) / -10) 0 calc(var(--sz) / 10) calc(var(--sz) / -10) var(--lg) inset,
  calc(var(--sz) / -50) calc(var(--sz) / 50) calc(var(--sz) / 30) 0 #fff2 inset, 
  0 0 calc(var(--sz) / 10) calc(var(--sz) / 50) #000c, 
  0 calc(var(--sz) / 4) calc(var(--sz) / 5) 0 #000d;
  */
  animation: grow2 calc(var(--sp) / 3) ease 0s 2 alternate;
}




@keyframes grow {
  80%, 100% {
    height: calc(calc(var(--sz) * 2) - calc(var(--sz) / 2.5));
    width: calc(calc(var(--sz) * 2) - calc(var(--sz) * -0.5));
  }
}

@keyframes grow2 {
  80%, 100% {
    height: calc(calc(var(--sz) * 2) - calc(var(--sz) / 2.5));
    width: calc(calc(var(--sz) * 2) - calc(var(--sz) * -0.5));
  }
}


.thumb:before {
  content: "";
  width: calc(var(--sz) / 1.65);
  height: calc(var(--sz) / 1.65);
  background: #fff0;
  border-radius: 100%;
  box-shadow: 
    0 calc(var(--sz) / -1) calc(var(--sz) / 2) var(--lg),
    0 calc(var(--sz) / 1) calc(var(--sz) / 2) var(--lg), 
    0 0 2vmin 0.25vmin var(--lg) inset, 0 0 5vmin 1.5vmin var(--lg), 
    0 0 calc(var(--sz) / 5) 0 #fff;
}






.lights {
  position: absolute;
  width: calc(100% + calc(var(--sz) * 2));
  height: calc(var(--sz) / 1.75);
  display: flex;
  justify-content: space-between;
  padding: 0;
  z-index: 0;
}

.lights span {
  background: #121212;
  position: relative;
  width: calc(var(--sz) / 1.75);
  height: calc(var(--sz) / 1.75);
  border-radius: var(--sz);
  box-shadow: 
    0 0 calc(var(--sz) / 50) calc(var(--sz) / 50) #0008, 
    0 calc(var(--sz) / -20) calc(var(--sz) / 10) calc(var(--sz) / 500) #000, 
    0 calc(var(--sz) / 20) calc(var(--sz) / 10) calc(var(--sz) / 500) #fff8, 
    0 0 calc(var(--sz) / 20) calc(var(--sz) / 25) #000;
  display: flex;
  align-items: center;
  justify-content: center;
}







.lights {
  position: absolute;
  width: calc(100% - calc(var(--sz) * 1.425));
  height: calc(var(--sz) / 1.75);
  display: flex;
  justify-content: space-between;
  padding: 0;
  z-index: 0;
  margin-top: -1px;
}

.lights span {
  background: #121212;
  position: relative;
  width: calc(var(--sz) / 1.75);
  height: calc(var(--sz) / 1.75);
  border-radius: var(--sz);
  box-shadow: 
    0 0 calc(var(--sz) / 50) calc(var(--sz) / 50) #0008, 
    0 calc(var(--sz) / -20) calc(var(--sz) / 10) calc(var(--sz) / 500) #000, 
    0 calc(var(--sz) / 20) calc(var(--sz) / 10) calc(var(--sz) / 500) #fff8, 
    0 0 calc(var(--sz) / 20) calc(var(--sz) / 25) #000;
  display: flex;
  align-items: center;
  justify-content: center;
}

.lights span:after {
  content: "";
  color: #fff;
  width: calc(100% - calc(var(--sz) / 15));
  height: calc(100% - calc(var(--sz) / 15));
  position: absolute;
  background: radial-gradient(circle at 50% 32%, #fff5 0 calc(var(--sz) / 20), #000 calc(var(--sz) / 3) calc(var(--sz) / 3));
  border-radius: var(--sz);
  top: calc(var(--sz) / 50);
}


/* off */
span.light-off:after {
  box-shadow: 
    0 0 calc(var(--sz) / 2.5) 0 var(--lg), 
    0 0 calc(var(--sz) / 3) calc(var(--sz) / 20) var(--lg) inset, 
    0 calc(var(--sz) / -20) calc(var(--sz) / 10) calc(var(--sz) / 10) #000 inset;
  background: radial-gradient(circle at 50% 32%, #fff 0 calc(var(--sz) / 20), #fff8 calc(var(--sz) / 3) calc(var(--sz) / 3));
}

#btn:checked + label + .lights span.light-off:after {
  box-shadow: 0 0 calc(var(--sz) / 3) 0 #f5000020, 0 0 calc(var(--sz) / 3) calc(var(--sz) / 20) #f5000020 inset;
  background: radial-gradient(circle at 50% 32%, #fff5 0 calc(var(--sz) / 20), #000 calc(var(--sz) / 3) calc(var(--sz) / 3));
}


/* on */
span.light-on:after {
  box-shadow: 0 0 calc(var(--sz) / 3) 0 #00f56d20, 0 0 calc(var(--sz) / 3) calc(var(--sz) / 20) #00f56d20 inset;
}

#btn:checked + label + .lights span.light-on:after {
  --lg: var(--on);
  box-shadow: 0 0 calc(var(--sz) / 2.5) 0 var(--lg), 0 0 calc(var(--sz) / 3) calc(var(--sz) / 20) var(--lg) inset, 0 calc(var(--sz) / -20) calc(var(--sz) / 10) calc(var(--sz) / 10) #000 inset;
  background: radial-gradient(circle at 50% 32%, #fff 0 calc(var(--sz) / 20), #fff2 calc(var(--sz) / 3) calc(var(--sz) / 3));
}

#btn:checked + label + .lights span.light-on:before {
  --lg: var(--on);
}

#btn:checked + label + .lights span.light-off:before {
  --lg: #666;
}
!

JS
!
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