#001523

CSS

:root {
  --oxford-by-night: #001523;
  --oxford-by-night-rgb: 0 21 35;
  --oxford-by-night-oklch: oklch(0.186 0.041 238.2);
}

.element {
  color: var(--oxford-by-night);
  background-color: hsl(204 100% 7%);
  border-color: oklch(0.186 0.041 238.2);
}

Tailwind CSS v4

@theme {
  --color-oxford-by-night: #001523;
  --color-oxford-by-night-50: #ebf7ff;
  --color-oxford-by-night-100: #dceaf5;
  --color-oxford-by-night-200: #c5d7e5;
  --color-oxford-by-night-300: #a5bbcb;
  --color-oxford-by-night-400: #88a2b4;
  --color-oxford-by-night-500: #6d8b9f;
  --color-oxford-by-night-600: #5c7586;
  --color-oxford-by-night-700: #4a5e6c;
  --color-oxford-by-night-800: #35454f;
  --color-oxford-by-night-900: #243037;
  --color-oxford-by-night-950: #131c22;
}

SCSS

$oxford-by-night: #001523;
$oxford-by-night-rgb: 0, 21, 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);
}