MDN CSS reference for properties, selectors, layout, and browser support notes.

https://developer.mozilla.org/en-US/docs/Web/CSS

*, *::before, *::after { box-sizing: border-box; }
html, body { height: 100%; }
body { margin: 0; font-family: system-ui, sans-serif; }
img, svg, video { max-width: 100%; height: auto; }

:root {
  color-scheme: light dark;
  --bg: #fff;
  --fg: #111;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0b0d10;
    --fg: #e6e6e6;
  }
}