* {
  box-sizing: border-box;
}
:root {
  --x: 0;
  --y: 0;
  --xp: 0;
  --yp: 0;
  --hue: calc(0 + (var(--xp) * 500));
  --bg: hsl(0 0% 10%);
  --size: 100px;
  --glow: radial-gradient(
      50% 50% at center,
      hsl(var(--hue) 80% 85%),
      hsl(var(--hue) 80% 70%),
      transparent
    )
    calc((var(--x) * 1px) - (var(--size) * 0.5))
    calc((var(--y) * 1px) - (var(--size) * 0.5)) / var(--size) var(--size)
    no-repeat fixed;
}

.controls {
  position: fixed;
  top: 2rem;
  right: 2rem;
}

body {
  display: flex;
  place-items: center;
  gap: 1rem;
  flex-wrap: wrap;
  justify-content: center;
  min-height: 100vh;
  font-family: "SF Pro Text", "SF Pro Icons", "AOS Icons", "Helvetica Neue",
    Helvetica, Arial, sans-serif, system-ui;
  background: var(--bg);
}

button {
  border-radius: 1rem;
  text-transform: uppercase;
  font-weight: bold;
  letter-spacing: 0.1ch;
  background: var(--bg);
  border: 4px solid transparent;
  box-shadow: 0 1px hsl(0 0% 100% / 0.15) inset;
  cursor: pointer;
  background: linear-gradient(var(--bg), var(--bg)) padding-box, var(--glow),
    linear-gradient(black, black) border-box;
  transition: cubic-bezier(2, 1, 1, 2) 0.24s;
  touch-action: none;
  position: relative;
  padding: 1rem 2rem;
}

button::before {
  content: "";
  position: absolute;
  inset: 0;
  box-shadow: 0 1px hsl(0 0% 100% / 0.15) inset;
  background: var(--bg);
  z-index: 2;
  border-radius: 1rem;
}

button span {
  background: var(--glow), black;
  background-clip: text;
  color: transparent;
  height: 100%;
  width: 100%;
  z-index: 2;
  position: relative;
  inset: 0;
}

:root:has(button:active) {
  --size: 300px;
}

button::after {
  content: "";
  position: absolute;
  inset: -4px;
  filter: blur(20px);
  border: 4px solid transparent;
  background: var(--glow);
  border-radius: 1rem;
}