#003553

CSS

:root {
  --sea-of-stars: #003553;
  --sea-of-stars-rgb: 0 53 83;
  --sea-of-stars-oklch: oklch(0.315 0.074 241.2);
}

.element {
  color: var(--sea-of-stars);
  background-color: hsl(202 100% 16%);
  border-color: oklch(0.315 0.074 241.2);
}

Tailwind CSS v4

@theme {
  --color-sea-of-stars: #003553;
  --color-sea-of-stars-50: #e4f8ff;
  --color-sea-of-stars-100: #d4ebff;
  --color-sea-of-stars-200: #bad9f2;
  --color-sea-of-stars-300: #97bcdb;
  --color-sea-of-stars-400: #77a4c6;
  --color-sea-of-stars-500: #588cb3;
  --color-sea-of-stars-600: #4b7797;
  --color-sea-of-stars-700: #3c5f79;
  --color-sea-of-stars-800: #294659;
  --color-sea-of-stars-900: #1c303e;
  --color-sea-of-stars-950: #0c1d28;
}

SCSS

$sea-of-stars: #003553;
$sea-of-stars-rgb: 0, 53, 83;
$sea-of-stars-light: mix(#fff, $sea-of-stars, 20%);
$sea-of-stars-dark: mix(#000, $sea-of-stars, 20%);

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