#13005B

CSS

:root {
  --the-vast-of-night: #13005b;
  --the-vast-of-night-rgb: 19 0 91;
  --the-vast-of-night-oklch: oklch(0.225 0.141 275.7);
}

.element {
  color: var(--the-vast-of-night);
  background-color: hsl(253 100% 18%);
  border-color: oklch(0.225 0.141 275.7);
}

Tailwind CSS v4

@theme {
  --color-the-vast-of-night: #13005b;
  --color-the-vast-of-night-50: #ebf2ff;
  --color-the-vast-of-night-100: #dce4ff;
  --color-the-vast-of-night-200: #c5cfff;
  --color-the-vast-of-night-300: #a6b0ff;
  --color-the-vast-of-night-400: #8896f1;
  --color-the-vast-of-night-500: #6e7ae2;
  --color-the-vast-of-night-600: #5d68be;
  --color-the-vast-of-night-700: #4a5399;
  --color-the-vast-of-night-800: #333d72;
  --color-the-vast-of-night-900: #232a51;
  --color-the-vast-of-night-950: #121736;
}

SCSS

$the-vast-of-night: #13005b;
$the-vast-of-night-rgb: 19, 0, 91;
$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);
}