#04192C

CSS

:root {
  --oxford-by-night: #04192c;
  --oxford-by-night-rgb: 4 25 44;
  --oxford-by-night-oklch: oklch(0.208 0.047 248);
}

.element {
  color: var(--oxford-by-night);
  background-color: hsl(209 83% 9%);
  border-color: oklch(0.208 0.047 248);
}

Tailwind CSS v4

@theme {
  --color-oxford-by-night: #04192c;
  --color-oxford-by-night-50: #ebf7ff;
  --color-oxford-by-night-100: #ddeaf7;
  --color-oxford-by-night-200: #c6d6e8;
  --color-oxford-by-night-300: #a6bacf;
  --color-oxford-by-night-400: #89a1b9;
  --color-oxford-by-night-500: #6e89a4;
  --color-oxford-by-night-600: #5d748b;
  --color-oxford-by-night-700: #4a5d6f;
  --color-oxford-by-night-800: #354452;
  --color-oxford-by-night-900: #242f39;
  --color-oxford-by-night-950: #131c23;
}

SCSS

$oxford-by-night: #04192c;
$oxford-by-night-rgb: 4, 25, 44;
$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);
}