<h1>Spotlight!</h1>

<div class="spotlight"></div>

@import url('https://fonts.googleapis.com/css2?family=Tagesschrift&display=swap');

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

body {
  font-family: "Tagesschrift", system-ui;
  min-height: 100vh;
  display: grid;
  place-items: center;
  background-image: linear-gradient(to bottom right, aquamarine, hotpink);
  color: white;
}

h1 {
  font-size: 8em;
}

.spotlight {
  position: fixed;
  inset: 0;
  opacity: 0.95;
  pointer-events: none;
  background-image: radial-gradient(circle at var(--clientX, 50%) var(--clientY, 50%), transparent 6em, black 8em);
}

document.body.addEventListener('mousemove', (e) => {
  document.body.style.setProperty('--clientX', e.clientX + 'px');
  document.body.style.setProperty('--clientY', e.clientY + 'px');
});