HTMLify

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

:root {
  --hue: 223;
  --bg: hsl(var(--hue), 10%, 90%);
  --fg: hsl(var(--hue), 10%, 10%);
  --light-sh: hsla(var(--hue), 10%, 95%, 0.5);
  --dark-sh: hsla(var(--hue), 10%, 15%, 0.4);
  --primary: hsl(var(--hue), 90%, 50%);
  --primary-t: hsla(var(--hue), 90%, 50%, 0);
  --trans-dur: 0.3s;
  font-size: 40px;
}

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

body {
  background-color: var(--bg);
  color: var(--fg);
  display: flex;
  height: 100vh;
  transition: background-color var(--trans-dur), color var(--trans-dur);
}

.switch,
.switch__input {
  -webkit-tap-highlight-color: transparent;
}

.switch {
  display: flex;
  gap: 0.5em;
  align-items: center;
  margin: auto;
}

.switch__icon,
.switch__icon-part {
  display: block;
}

.switch__icon {
  position: relative;
  width: 1em;
  height: 1em;
  transition: filter var(--trans-dur);
}

.switch__icon-part {
  background-color: hsla(var(--hue), 10%, 10%, 0.3);
  position: absolute;
  transition: background-color var(--trans-dur), box-shadow var(--trans-dur);
}

.switch__icon--light {
  filter: drop-shadow(0 0 0.125em hsla(var(--hue), 90%, 70%, 0.2));
}

.switch__icon--light .switch__icon-part {
  background-color: hsla(var(--hue), 90%, 70%, 1);
  border-radius: 0.125em;
  top: 50%;
  left: 50%;
  width: 0.125em;
  height: 0.2em;
  transform-origin: 50% 0;
}

.switch__icon--light .switch__icon-part--1 {
  border-radius: 50%;
  box-shadow: 0 0.0625em 0.0625em var(--dark-sh) inset,
    0 0.0625em 0.0625em var(--light-sh);
  top: 0.3em;
  left: 0.3em;
  width: 0.4em;
  height: 0.4em;
}

.switch__icon--light .switch__icon-part--2 {
  box-shadow: 0 0.0625em 0.0625em var(--dark-sh) inset,
    0 0.0625em 0.0625em var(--light-sh);
  transform: translateX(-50%) rotate(0) translateY(0.3em);
}

.switch__icon--light .switch__icon-part--3 {
  box-shadow: 0.0625em 0.0625em 0.0625em var(--dark-sh) inset,
    0.0625em 0.0625em 0.0625em var(--light-sh);
  transform: translateX(-50%) rotate(45deg) translateY(0.3em);
}

.switch__icon--light .switch__icon-part--4 {
  box-shadow: 0.0625em 0 0.0625em var(--dark-sh) inset,
    0.0625em 0 0.0625em var(--light-sh);
  transform: translateX(-50%) rotate(90deg) translateY(0.3em);
}

.switch__icon--light .switch__icon-part--5 {
  box-shadow: 0.0625em -0.0625em 0.0625em var(--dark-sh) inset,
    0.0625em -0.0625em 0.0625em var(--light-sh);
  transform: translateX(-50%) rotate(135deg) translateY(0.3em);
}

.switch__icon--light .switch__icon-part--6 {
  box-shadow: 0 -0.0625em 0.0625em var(--dark-sh) inset,
    0 -0.0625em 0.0625em var(--light-sh);
  transform: translateX(-50%) rotate(180deg) translateY(0.3em);
}

.switch__icon--light .switch__icon-part--7 {
  box-shadow: -0.0625em -0.0625em 0.0625em var(--dark-sh) inset,
    -0.0625em -0.0625em 0.0625em var(--light-sh);
  transform: translateX(-50%) rotate(225deg) translateY(0.3em);
}

.switch__icon--light .switch__icon-part--8 {
  box-shadow: -0.0625em 0 0.0625em var(--dark-sh) inset,
    -0.0625em 0 0.0625em var(--light-sh);
  transform: translateX(-50%) rotate(270deg) translateY(0.3em);
}

.switch__icon--light .switch__icon-part--9 {
  box-shadow: -0.0625em 0.0625em 0.0625em var(--dark-sh) inset,
    -0.0625em 0.0625em 0.0625em var(--light-sh);
  transform: translateX(-50%) rotate(315deg) translateY(0.3em);
}

.switch__icon--dark {
  filter: drop-shadow(0 0 0.125em hsla(var(--hue), 90%, 70%, 0)) drop-shadow(0 0.0625em 0.0625em var(--light-sh));
}

.switch__icon--dark .switch__icon-part--1 {
  background-color: transparent;
  border-radius: 50%;
  clip-path: url(#moon);
  overflow: hidden;
  width: 100%;
  height: 100%;
}

.switch__icon--dark .switch__icon-part--1a {
  border-radius: 50%;
  box-shadow: 0 0.0625em 0.0625em var(--dark-sh) inset;
  width: 100%;
  height: 100%;
}

.switch__icon--dark .switch__icon-part--1b {
  background-color: transparent;
  border-radius: 50%;
  width: 100%;
  height: 100%;
}

.switch__icon--dark .switch__icon-part--1b::before {
  background-color: var(--bg);
  border-radius: 50%;
  box-shadow: 0 0.0625em 0.0625em var(--dark-sh),
    0 0.0625em 0.0625em var(--light-sh) inset;
  content: "";
  display: block;
  position: absolute;
  right: 0;
  left: auto;
  transition: background-color var(--trans-dur);
  width: 62.5%;
  height: 62.5%;
}

.switch__input {
  background-color: hsla(var(--hue), 10%, 10%, 0.1);
  border-radius: 0.75em;
  box-shadow: 0 0.0625em 0.125em var(--dark-sh) inset,
    0 0.0625em 0.125em var(--light-sh), 0 0 0 0.125em var(--primary-t);
  display: block;
  outline: transparent;
  position: relative;
  width: 2.5em;
  height: 1.5em;
  transition: box-shadow var(--trans-dur);
  -webkit-appearance: none;
  appearance: none;
  cursor: pointer;
}

.switch__input:focus-visible {
  box-shadow: 0 0.0625em 0.125em var(--dark-sh) inset,
    0 0.0625em 0.125em var(--light-sh), 0 0 0 0.125em var(--primary);
}

.switch__input::before {
  background-color: var(--primary);
  border-radius: 50%;
  box-shadow: 0 0.0625em 0.125em hsla(var(--hue), 10%, 10%, 0.5);
  content: "";
  display: block;
  position: absolute;
  top: 0.25em;
  left: 0.25em;
  width: 1em;
  height: 1em;
  transition: background-color var(--trans-dur), box-shadow var(--trans-dur),
    transform var(--trans-dur) cubic-bezier(0.65, 0.05, 0.34, 1);  
}

.switch__input:checked::before {
  transform: translateX(1em);
}

.switch__label {
  overflow: hidden;
  position: absolute;
  width: 1px;
  height: 1px;
}

/* Dark theme */
body:has(.switch__input:checked) {
  --bg: hsl(var(--hue), 10%, 30%);
  --fg: hsl(var(--hue), 10%, 90%);
  --light-sh: hsla(var(--hue), 10%, 55%, 0.5);
  --dark-sh: hsla(var(--hue), 10%, 15%, 0.4);
  --primary: hsl(var(--hue), 90%, 60%);
}

body:has(.switch__input:checked) .switch__icon--light {
  filter: drop-shadow(0 0 0.125em hsla(var(--hue), 90%, 75%, 0));
}

body:has(.switch__input:checked) .switch__icon--light .switch__icon-part {
  background-color: hsla(var(--hue), 10%, 10%, 0.3);
}

body:has(.switch__input:checked) .switch__icon--dark {
  filter: drop-shadow(0 0 0.125em hsla(var(--hue), 90%, 75%, 0.6)) drop-shadow(0 0.0625em 0.0625em var(--light-sh));
}

body:has(.switch__input:checked) .switch__icon--dark .switch__icon-part--1a {
  background-color: hsla(var(--hue), 90%, 75%, 1);
}