:root,
:root[color-theme="light"] {
  --header-background: #4a7;
  --footer-background: #243;
}
@media (prefers-color-scheme: light) {
  :root {
    --header-background: #4a7;
    --footer-background: #243;
  }
}

:root[color-theme="dark"] {
  --header-background: #4a7;
  --footer-background: #243;
}
@media (prefers-color-scheme: dark) {
  :root {
    --header-background: #4a7;
    --footer-background: #243;
  }
}