#001221

CSS

:root {
  --oxford-by-night: #001221;
  --oxford-by-night-rgb: 0 18 33;
  --oxford-by-night-oklch: oklch(0.175 0.042 242.4);
}

.element {
  color: var(--oxford-by-night);
  background-color: hsl(207 100% 6%);
  border-color: oklch(0.175 0.042 242.4);
}

Tailwind CSS v4

@theme {
  --color-oxford-by-night: #001221;
  --color-oxford-by-night-50: #ecf7ff;
  --color-oxford-by-night-100: #ddeaf5;
  --color-oxford-by-night-200: #c6d7e5;
  --color-oxford-by-night-300: #a6bacc;
  --color-oxford-by-night-400: #8aa2b6;
  --color-oxford-by-night-500: #6e8aa0;
  --color-oxford-by-night-600: #5e7587;
  --color-oxford-by-night-700: #4b5d6c;
  --color-oxford-by-night-800: #354550;
  --color-oxford-by-night-900: #242f37;
  --color-oxford-by-night-950: #131c22;
}

SCSS

$oxford-by-night: #001221;
$oxford-by-night-rgb: 0, 18, 33;
$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);
}