body {
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  gap: 3rem;
  overflow: hidden;
  margin: 0;
  min-height: 100vh;
  box-sizing: border-box;
  background-image: linear-gradient(45deg, #223, #112);
  background:
    radial-gradient(at 100% 0, #fff2, #fff0 50%),
    radial-gradient(at 0% 100%, #0002, #0000 50%),
    #545153;
}

@property --x {
  syntax: '<angle>';
  inherits: true;
  initial-value: 1deg;
}

@property --c {
  syntax: '<color>';
  inherits: true;
  initial-value: #0000;
}

.neon {
  --x: 1deg;
  --c: #0000;
  --color: #0ff;
  font-size: 3rem;
  appearance: none;
  position: relative;
  aspect-ratio: 2;
  border-radius: 100em;
  background: 
    linear-gradient(to bottom right, #0001, #0000),
    #444143;
  width: 3em;
  box-shadow:
    inset 0 0 0.25em -0.25em #0008,
    inset 0.05em 0.05em 0.2em #000811,
    inset -0.05em -0.05em 0.15em 0.05em #ccc1,
    0 0 0 0.11em #545153;
  transition: --x 0.5s, --c 0.5s, box-shadow 0.5s;
  filter: drop-shadow(0 0 0.2em var(--c));
}

/* BEFORE */
.neon::before {
  content: "";
  position: absolute;
  height: 80%;
  aspect-ratio: 1;
  top: 50%;
  left: 25%;
  transform: translate(-50%, -50%);
  background: 
    radial-gradient(#0000 15%, #343133 16%, #545153 20%),
    repeating-linear-gradient(#0000 0 10%, #0002 0 20%) 50% 50% / 25% 25% no-repeat,
    repeating-linear-gradient(90deg, #0000 0 10%, #0002 0 20%) 50% 50% / 25% 25% no-repeat,
    radial-gradient(var(--c) 17%, #0000 0),
    #545153;
  box-shadow:
    inset -0.05em -0.05em 0.1em #0008,
    inset 0.05em 0.05em 0.1em #ffffff22,
    inset 0.05em 0em 0.1em -0.065em var(--c),
    0.1em 0.1em 0.15em #000c;
  border-radius: 50%;
  transition: left 0.5s, box-shadow 0.1s;
}

/* AFTER */
.neon::after {
  content: "";
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: calc(100% + 0.25em);
  height: calc(100% + 0.25em);
  border: 0.1em solid var(--color);
  border-radius: 100em;
  -webkit-mask: conic-gradient(from calc(270deg - var(--x)), #000 calc(2 * var(--x)), #0001 0);
  box-shadow: 0 0 0 2em #0000;
}

/* HOVER */
.neon:hover {
  --x: 3deg;
  --c: rgb(0 255 255 / 25%);
  box-shadow:
    inset 0 0 0.25em -0.25em #0008,
    inset 0.05em 0.05em 0.2em #000811,
    inset -0.05em -0.05em 0.15em 0.05em #ccc1,
    0 0 0.05em 0.075em #545153;
}

/* CHECKED */
.neon:checked {
  --x: 180deg;
  --c: var(--color);
  box-shadow:
    inset 0 0 0.25em -0.25em #0008,
    inset 0.05em 0.05em 0.2em #000811,
    inset -0.05em -0.05em 0.15em 0.05em #ccc1,
    0 0 0.1em 0.05em #545153;
}

.neon:checked::before {
  left: 75%;
  box-shadow:
    inset -0.05em -0.05em 0.1em #0008,
    inset 0.05em 0.05em 0.1em #ffffff22,
    inset -0.05em 0em 0.1em -0.035em var(--c),
    0.1em 0.1em 0.15em #000c;
}

/* DISABLED */
.neon:disabled {
  opacity: 0.25;
}

/* PRINT */
@media print {
  .neon {
    background: none;
  }
  .neon,
  .neon::before,
  .neon::after {
    -webkit-print-color-adjust: exact;
    print-color-adjust: exact;
  }
}

/* REDUCED MOTION */
@media (prefers-reduced-motion) {
  .neon,
  .neon::before,
  .neon::after {
    transition: none !important;
    animation: none !important;
  }
}