<select class="theme reveal">
  <option value="auto">Auto</opation>
  <option value="dark">Dark</opation>
  <option value="light">Light</opation>
</select>

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

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

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

:root {
  color-scheme: light dark;

  --spotlight-cover: light-dark(white, black);
  --spotlight-reveal: light-dark(black, white);

  @media (prefers-color-scheme: dark) {
    --spotlight-blend-mode: darken;
  }
  
  @media (prefers-color-scheme: light) {
    --spotlight-blend-mode: lighten;
  }

  &:has(.theme option[value="dark"]:checked) {
    color-scheme: dark;
    --spotlight-blend-mode: darken;
  }  
  
  &:has(.theme option[value="light"]:checked) {
    color-scheme: light;
    --spotlight-blend-mode: lighten;
  }
}

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

select {
  font: inherit;
  padding: 1em 2em;
}

.spotlight {
  position: fixed;
  inset: 0;
  pointer-events: none;
  filter: blur(0.5em) contrast(10);
  mix-blend-mode: var(--spotlight-blend-mode);
  background-color: var(--spotlight-reveal);
  outline: 2em solid var(--spotlight-cover);
  background-image:
    radial-gradient(circle at var(--clientX, 50%) var(--clientY, 50%), transparent 6em, var(--spotlight-cover) 8em),
    repeating-conic-gradient(from -20deg, var(--spotlight-cover) 0 40deg, transparent 0 180deg);
  background-size: 100% 100%, 4em 4em;
  background-position: 0 0, calc(var(--clientX, 50%) * 1.5) calc(var(--clientY, 50%) * 1.5);
  transition: opacity 1s, background-color 1s;

  body:has(.reveal:hover) & {
    opacity: 0;
    background-color: var(--spotlight-cover);
  }
}

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