#002239

CSS

:root {
  --oxford-by-night: #002239;
  --oxford-by-night-rgb: 0 34 57;
  --oxford-by-night-oklch: oklch(0.242 0.058 243);
}

.element {
  color: var(--oxford-by-night);
  background-color: hsl(204 100% 11%);
  border-color: oklch(0.242 0.058 243);
}

Tailwind CSS v4

@theme {
  --color-oxford-by-night: #002239;
  --color-oxford-by-night-50: #e8f7ff;
  --color-oxford-by-night-100: #d8ebfb;
  --color-oxford-by-night-200: #c0d8ec;
  --color-oxford-by-night-300: #9fbbd4;
  --color-oxford-by-night-400: #81a3bf;
  --color-oxford-by-night-500: #648baa;
  --color-oxford-by-night-600: #557690;
  --color-oxford-by-night-700: #445e73;
  --color-oxford-by-night-800: #304555;
  --color-oxford-by-night-900: #20303b;
  --color-oxford-by-night-950: #101c25;
}

SCSS

$oxford-by-night: #002239;
$oxford-by-night-rgb: 0, 34, 57;
$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);
}