HTMLify

* {
  border: 0;
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

:root {
  --hue: 223;
  --off-hue: 3;
  --on-hue1: 123;
  --on-hue2: 168;
  --fg: hsl(var(--hue), 10%, 90%);
  --primary: hsl(var(--hue), 90%, 50%);
  --trans-dur: 0.6s;
  --trans-timing: cubic-bezier(0.65, 0, 0.35, 1);
  font-size: calc(40px + 20 * (100vw - 320px) / 2240);
}

body,
input {
  font: 1em/1.5 sans-serif;
}

body {
  background-image: linear-gradient(45deg, hsl(var(--hue), 10%, 20%), hsl(var(--hue), 10%, 10%));
  color: var(--fg);
  display: flex;
  height: 100vh;
  transition: background-color var(--trans-dur), color var(--trans-dur);
}

.switch,
.switch__input {
  -webkit-tap-highlight-color: rgba(0, 0, 0, 0);
}

.switch {
  display: block;
  margin: auto;
  position: relative;
  width: 5em;
  height: 3em;
  cursor: pointer;
}
.switch__base-outer, .switch__base-inner {
  display: block;
  position: absolute;
}
.switch__base-outer {
  border-radius: 1.25em;
  box-shadow: -0.125em -0.125em 0.25em hsl(var(--hue), 10%, 30%), 0.125em 0.125em 0.125em hsl(var(--hue), 10%, 30%) inset, 0.125em 0.125em 0.25em hsl(0deg, 0%, 0%), -0.125em -0.125em 0.125em hsl(var(--hue), 10%, 5%) inset;
  top: 0.125em;
  left: 0.125em;
  width: 4.75em;
  height: 2.75em;
}
.switch__base-inner {
  border-radius: 1.125em;
  box-shadow: -0.25em -0.25em 0.25em hsl(var(--hue), 10%, 30%) inset, 0.0625em 0.0625em 0.125em hsla(var(--hue), 10%, 30%), 0.125em 0.25em 0.25em hsl(var(--hue), 10%, 5%) inset, -0.0625em -0.0625em 0.125em hsla(var(--hue), 10%, 5%);
  top: 0.375em;
  left: 0.375em;
  width: 4.25em;
  height: 2.25em;
}
.switch__base-neon {
  display: block;
  overflow: visible;
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: auto;
}
.switch__base-neon path {
  stroke-dasharray: 0 104.26 0;
  transition: stroke-dasharray var(--trans-dur) var(--trans-timing);
}
.switch__input {
  outline: transparent;
  position: relative;
  width: 100%;
  height: 100%;
  -webkit-appearance: none;
  appearance: none;
}
.switch__input:before {
  border-radius: 0.125em;
  box-shadow: 0 0 0 0.125em hsla(var(--hue), 90%, 50%, 0);
  content: "";
  display: block;
  position: absolute;
  inset: -0.125em;
  transition: box-shadow 0.15s linear;
}
.switch__input:focus-visible:before {
  box-shadow: 0 0 0 0.125em var(--primary);
}
.switch__knob, .switch__knob-container {
  border-radius: 1em;
  display: block;
  position: absolute;
}
.switch__knob {
  background-color: hsl(var(--hue), 10%, 15%);
  background-image: radial-gradient(88% 88% at 50% 50%, hsl(var(--hue), 10%, 20%) 47%, hsla(var(--hue), 10%, 20%, 0) 50%), radial-gradient(88% 88% at 47% 47%, hsl(var(--hue), 10%, 85%) 45%, hsla(var(--hue), 10%, 85%, 0) 50%), radial-gradient(65% 70% at 40% 60%, hsl(var(--hue), 10%, 20%) 46%, hsla(var(--hue), 10%, 20%, 0) 50%);
  box-shadow: -0.0625em -0.0625em 0.0625em hsl(var(--hue), 10%, 15%) inset, -0.125em -0.125em 0.0625em hsl(var(--hue), 10%, 5%) inset, 0.75em 0.25em 0.125em hsla(0deg, 0%, 0%, 0.8);
  width: 2em;
  height: 2em;
  transition: transform var(--trans-dur) var(--trans-timing);
}
.switch__knob-container {
  overflow: hidden;
  top: 0.5em;
  left: 0.5em;
  width: 4em;
  height: 2em;
}
.switch__knob-neon {
  display: block;
  width: 2em;
  height: auto;
}
.switch__knob-neon circle {
  opacity: 0;
  stroke-dasharray: 0 90.32 0 54.19;
  transition: opacity var(--trans-dur) steps(1, end), stroke-dasharray var(--trans-dur) var(--trans-timing);
}
.switch__knob-shadow {
  border-radius: 50%;
  box-shadow: 0.125em 0.125em 0.125em hsla(0deg, 0%, 0%, 0.9);
  display: block;
  position: absolute;
  top: 0.5em;
  left: 0.5em;
  width: 2em;
  height: 2em;
  transition: transform var(--trans-dur) var(--trans-timing);
}
.switch__led {
  background-color: hsl(var(--off-hue), 90%, 70%);
  border-radius: 50%;
  box-shadow: 0 -0.0625em 0.0625em hsl(var(--off-hue), 90%, 40%) inset, 0 0 0.125em hsla(var(--off-hue), 90%, 70%, 0.3), 0 0 0.125em hsla(var(--off-hue), 90%, 70%, 0.3), 0.125em 0.125em 0.125em hsla(0deg, 0%, 0%, 0.5);
  display: block;
  position: absolute;
  top: 0;
  left: 0;
  width: 0.25em;
  height: 0.25em;
  transition: background-color var(--trans-dur) var(--trans-timing), box-shadow var(--trans-dur) var(--trans-timing);
}
.switch__text {
  overflow: hidden;
  position: absolute;
  width: 1px;
  height: 1px;
}
.switch__input:checked ~ .switch__led {
  background-color: hsl(var(--on-hue1), 90%, 70%);
  box-shadow: 0 -0.0625em 0.0625em hsl(var(--on-hue1), 90%, 40%) inset, 0 -0.125em 0.125em hsla(var(--on-hue1), 90%, 70%, 0.3), 0 0.125em 0.125em hsla(var(--on-hue1), 90%, 70%, 0.3), 0.125em 0.125em 0.125em hsla(0deg, 0%, 0%, 0.5);
}
.switch__input:checked ~ .switch__base-neon path {
  stroke-dasharray: 52.13 0 52.13;
}
.switch__input:checked ~ .switch__knob-shadow, .switch__input:checked ~ .switch__knob-container .switch__knob {
  transform: translateX(100%);
}
.switch__input:checked ~ .switch__knob-container .switch__knob-neon circle {
  opacity: 1;
  stroke-dasharray: 45.16 0 45.16 54.19;
  transition-timing-function: steps(1, start), var(--trans-timing);
}