#021323

CSS

:root {
  --oxford-by-night: #021323;
  --oxford-by-night-rgb: 2 19 35;
  --oxford-by-night-oklch: oklch(0.181 0.042 246.7);
}

.element {
  color: var(--oxford-by-night);
  background-color: hsl(209 89% 7%);
  border-color: oklch(0.181 0.042 246.7);
}

Tailwind CSS v4

@theme {
  --color-oxford-by-night: #021323;
  --color-oxford-by-night-50: #ecf6ff;
  --color-oxford-by-night-100: #dee9f6;
  --color-oxford-by-night-200: #c7d6e6;
  --color-oxford-by-night-300: #a7bacc;
  --color-oxford-by-night-400: #8ba1b6;
  --color-oxford-by-night-500: #7089a1;
  --color-oxford-by-night-600: #5f7488;
  --color-oxford-by-night-700: #4c5d6d;
  --color-oxford-by-night-800: #364450;
  --color-oxford-by-night-900: #252f38;
  --color-oxford-by-night-950: #141c22;
}

SCSS

$oxford-by-night: #021323;
$oxford-by-night-rgb: 2, 19, 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);
}