#0A025D

CSS

:root {
  --the-vast-of-night: #0a025d;
  --the-vast-of-night-rgb: 10 2 93;
  --the-vast-of-night-oklch: oklch(0.225 0.144 269.6);
}

.element {
  color: var(--the-vast-of-night);
  background-color: hsl(245 96% 19%);
  border-color: oklch(0.225 0.144 269.6);
}

Tailwind CSS v4

@theme {
  --color-the-vast-of-night: #0a025d;
  --color-the-vast-of-night-50: #e6f4ff;
  --color-the-vast-of-night-100: #d6e6ff;
  --color-the-vast-of-night-200: #bed1ff;
  --color-the-vast-of-night-300: #9db3ff;
  --color-the-vast-of-night-400: #7d99f3;
  --color-the-vast-of-night-500: #617ee5;
  --color-the-vast-of-night-600: #526bc1;
  --color-the-vast-of-night-700: #41559b;
  --color-the-vast-of-night-800: #2c3f74;
  --color-the-vast-of-night-900: #1e2b52;
  --color-the-vast-of-night-950: #0e1837;
}

SCSS

$the-vast-of-night: #0a025d;
$the-vast-of-night-rgb: 10, 2, 93;
$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);
}