#031623

CSS

:root {
  --oxford-by-night: #031623;
  --oxford-by-night-rgb: 3 22 35;
  --oxford-by-night-oklch: oklch(0.191 0.037 239.9);
}

.element {
  color: var(--oxford-by-night);
  background-color: hsl(204 84% 7%);
  border-color: oklch(0.191 0.037 239.9);
}

Tailwind CSS v4

@theme {
  --color-oxford-by-night: #031623;
  --color-oxford-by-night-50: #ecf7ff;
  --color-oxford-by-night-100: #deeaf4;
  --color-oxford-by-night-200: #c7d7e3;
  --color-oxford-by-night-300: #a7bac9;
  --color-oxford-by-night-400: #8ba2b3;
  --color-oxford-by-night-500: #708a9d;
  --color-oxford-by-night-600: #5f7585;
  --color-oxford-by-night-700: #4c5d6a;
  --color-oxford-by-night-800: #37444e;
  --color-oxford-by-night-900: #252f36;
  --color-oxford-by-night-950: #141c21;
}

SCSS

$oxford-by-night: #031623;
$oxford-by-night-rgb: 3, 22, 35;
$oxford-by-night-light: mix(#fff, $oxford-by-night, 20%);
$oxford-by-night-dark: mix(#000, $oxford-by-night, 20%);

.element {
  color: $oxford-by-night;
  box-shadow: 0 0 0 2px rgba($oxford-by-night, 0.35);
}