Code Playground

@charset "UTF-8";
@import url(https://fonts.googleapis.com/css?family=Nunito+Sans:300,400,600,700,800);
*,
:after,
:before {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}
body {
  background: #1f1f23;
  margin: 0;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  font-size: 5em;
  gap: 0.5em;
}

@property --color {
  syntax: '<color>';
  inherits: true;
  initial-value: red;
}
@property --light-on {
  syntax: '<color>';
  inherits: true;
  initial-value: #0001;
}
@property --light-off {
  syntax: '<color>';
  inherits: true;
  initial-value: #000d;
}

@keyframes squeeze {
  0%, 100% { width: 0.95em; aspect-ratio: 1;  }
  50% { width: 1.35em; aspect-ratio: 1.75; }
}
@keyframes squeeze2 {
  0%, 100% { width: 0.95em; aspect-ratio: 1;  }
  50% { width: 1.35em; aspect-ratio: 1.75; }
}

.ellastic {
  --on: #af5;
  --off: #d55;
  --duration: 0.75s;
  --color: var(--off);
  --color-semi: color-mix(in srgb, var(--color) 50%, #0000);
  --color-semi2: color-mix(in srgb, var(--color) 33%, #0000);
  --color-semi3: color-mix(in srgb, var(--color) 15%, #fff0);
  --light-on: #0001;
  --light-off: #000d;
  appearance: none;
  font-size: 1em;
  width: 2.5em;
  aspect-ratio: 2.5;
  border-radius: 3em;
  border: 1px solid #0000;
  position: relative;
  color: var(--color);
  filter: 
    drop-shadow(0 0.025em 0.0125em #fff3)
    drop-shadow(0 -0.025em 0.0125em #000c)
    ;
  transition: 
    --color var(--duration) linear,
    --light-on calc(var(--duration) / 2),
    --light-off calc(var(--duration) / 2),
    color var(--duration) linear;
  atransition-delay: 0s, calc(var(--duration) / 1), 0s, 0s;

&::after {
    content: "";
    position: absolute;
    top: 50%;
    left: 0.5em;
    transform: translate(-50%, -50%);
    width: 0.95em;
    aspect-ratio: 1;
    border-radius: 5em;
    border: 1px solid #0000;
    background: 
      radial-gradient(at 50% 0, var(--color-semi), #0000 40%),
      radial-gradient(at 50% 100%, var(--color-semi), #0000 40%),
      radial-gradient(50% 50% at 50% 0, #fff2, #0000 90%),
      radial-gradient(50% 50% at 50% 110%, #0007, #0000 90%),
      radial-gradient(circle, #0000 0.12em, var(--color-semi3) 0.125em, #0000 0.5em),
      radial-gradient(circle, #0000 0.12em, var(--color-semi2) 0.125em, #0000 0.4em),
      radial-gradient(circle, #0000 0.12em, #fff1 0.125em, #fff0 0.25em),
      radial-gradient(circle, #0000 0.12em, #2f2f33 0.125em);
    ;
    background-repeat: no-repeat;
    box-shadow: 
      inset 0 0 0.125em var(--color-semi),
      0 0 0.2em #0005,
      0 0.15em 0.1em #0008;
    transition: left var(--duration) linear;
    animation: squeeze var(--duration) 1 linear forwards;
  }

&::before {
    content: "";
    position: absolute;
    top: -1px;
    left: -1px;
    width: calc(100% + 2px);
    height: calc(100% + 2px);
    -webkit-mask:
      radial-gradient(45% 75% at 50% -50%, #0000 99%, #000) 50% 0 / 2em 0.2em no-repeat,
      radial-gradient(45% 75% at 50% 150%, #0000 99%, #000) 50% 100% / 2em 0.2em no-repeat,
      linear-gradient(90deg, #000 0.55em, #0000 0 1.95em, #000 0),
      linear-gradient(#000 0 0) 50% 50% / 2em 0.75em no-repeat
      ;
    border-radius: 3em;
    background: 
      /* left light */
      radial-gradient(circle at 0.505em 50%, #0004, var(--light-on) 0.11em, #0000 0.12em),
      radial-gradient(50% 100% at 0.505em 45%, #fff9 0.025em, #fff0 0.08em),

radial-gradient(circle at 0.505em 50%, #0000 0.025em, #0008 0.12em, #0000 0.13em),
      radial-gradient(circle at 0.505em 50%, var(--off) 0.11em, #0000 0.12em),
      radial-gradient(circle at 0.505em 50%, #000 0.10em, #0000 0.16em),
      radial-gradient(circle at 0.505em 49%, #000 0.12em, #fff0 0.13em),
      radial-gradient(circle at 0.505em 51%, #fff7 0.12em, #fff0 0.13em),
      /* right light */
      radial-gradient(circle at 2.005em 50%, #0004, var(--light-off) 0.11em, #0000 0.12em),
      radial-gradient(50% 100% at 2.005em 45%, #fff9 0.025em, #fff0 0.08em),
      radial-gradient(circle at 2.005em 50%, #0000 0.025em, #0008 0.12em, #0000 0.13em),
      radial-gradient(circle at 2.005em 50%, var(--on) 0.11em, #0000 0.12em),
      radial-gradient(circle at 2.005em 50%, #000 0.10em, #0000 0.16em),
      radial-gradient(circle at 2.005em 49%, #000 0.12em, #fff0 0.13em),
      radial-gradient(circle at 2.005em 51%, #fff7 0.12em, #fff0 0.13em),
      /* background base */
      radial-gradient(45% 100% at 50% 130%, #0007 50%, #0000) 50% 100% / 2em 0.2em no-repeat,
      radial-gradient(45% 100% at 50% -30%, #0007 50%, #0000) 50% 0% / 2em 0.2em no-repeat,
      #0c0c10a0;
    box-shadow:
      inset 0 0 0.1em 0.005em #000,
      inset 0 0 0.25em #0007
  }

&:checked {
    --color: var(--on); 
    --light-on: #000d;
    --light-off: #0001;
    atransition-delay: 0s, 0s, calc(var(--duration) / 1), 0s;

&::after {
      left: 2em;
      animation: squeeze2 var(--duration) 1 linear forwards;
    }
  }

&[disabled] {
    --on: #aaa;
    --off: #aaa;
    &, &::before, &::after {
      transition-duration: 0s !important;
      animation-duration: 0s !important;
    }
  }
}

@media print {
  .ellastic {
    &, &::before, &::after {
      -webkit-print-color-adjust: exact;
      print-color-adjust: exact;
    }
  }
}

@media (prefers-reduced-motion) {
  .ellastic {
    &, &::before, &::after {
      transition-duration: 0s !important;
      animation-duration: 0s !important;
    }
  }
}

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