#0A009C

CSS

:root {
  --everlasting-night: #0a009c;
  --everlasting-night-rgb: 10 0 156;
  --everlasting-night-oklch: oklch(0.316 0.215 266);
}

.element {
  color: var(--everlasting-night);
  background-color: hsl(244 100% 31%);
  border-color: oklch(0.316 0.215 266);
}

Tailwind CSS v4

@theme {
  --color-everlasting-night: #0a009c;
  --color-everlasting-night-50: #dbf4ff;
  --color-everlasting-night-100: #c9e6ff;
  --color-everlasting-night-200: #add0ff;
  --color-everlasting-night-300: #88b0ff;
  --color-everlasting-night-400: #6294ff;
  --color-everlasting-night-500: #4275ff;
  --color-everlasting-night-600: #3964e6;
  --color-everlasting-night-700: #2d50b9;
  --color-everlasting-night-800: #1a3b8b;
  --color-everlasting-night-900: #102963;
  --color-everlasting-night-950: #041544;
}

SCSS

$everlasting-night: #0a009c;
$everlasting-night-rgb: 10, 0, 156;
$everlasting-night-light: mix(#fff, $everlasting-night, 20%);
$everlasting-night-dark: mix(#000, $everlasting-night, 20%);

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