#0C005F

CSS

:root {
  --the-vast-of-night: #0c005f;
  --the-vast-of-night-rgb: 12 0 95;
  --the-vast-of-night-oklch: oklch(0.226 0.148 270.5);
}

.element {
  color: var(--the-vast-of-night);
  background-color: hsl(248 100% 19%);
  border-color: oklch(0.226 0.148 270.5);
}

Tailwind CSS v4

@theme {
  --color-the-vast-of-night: #0c005f;
  --color-the-vast-of-night-50: #e6f3ff;
  --color-the-vast-of-night-100: #d7e6ff;
  --color-the-vast-of-night-200: #bed1ff;
  --color-the-vast-of-night-300: #9eb2ff;
  --color-the-vast-of-night-400: #7e98f5;
  --color-the-vast-of-night-500: #627de7;
  --color-the-vast-of-night-600: #536ac3;
  --color-the-vast-of-night-700: #42559d;
  --color-the-vast-of-night-800: #2d3e75;
  --color-the-vast-of-night-900: #1e2b53;
  --color-the-vast-of-night-950: #0e1837;
}

SCSS

$the-vast-of-night: #0c005f;
$the-vast-of-night-rgb: 12, 0, 95;
$the-vast-of-night-light: mix(#fff, $the-vast-of-night, 20%);
$the-vast-of-night-dark: mix(#000, $the-vast-of-night, 20%);

.element {
  color: $the-vast-of-night;
  box-shadow: 0 0 0 2px rgba($the-vast-of-night, 0.35);
}