#001421

CSS

:root {
  --oxford-by-night: #001421;
  --oxford-by-night-rgb: 0 20 33;
  --oxford-by-night-oklch: oklch(0.181 0.04 237);
}

.element {
  color: var(--oxford-by-night);
  background-color: hsl(204 100% 6%);
  border-color: oklch(0.181 0.04 237);
}

Tailwind CSS v4

@theme {
  --color-oxford-by-night: #001421;
  --color-oxford-by-night-50: #ebf7ff;
  --color-oxford-by-night-100: #dceaf4;
  --color-oxford-by-night-200: #c6d7e4;
  --color-oxford-by-night-300: #a6bbca;
  --color-oxford-by-night-400: #89a2b3;
  --color-oxford-by-night-500: #6e8b9d;
  --color-oxford-by-night-600: #5d7585;
  --color-oxford-by-night-700: #4a5e6b;
  --color-oxford-by-night-800: #35454e;
  --color-oxford-by-night-900: #243036;
  --color-oxford-by-night-950: #131c21;
}

SCSS

$oxford-by-night: #001421;
$oxford-by-night-rgb: 0, 20, 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);
}