#003657

CSS

:root {
  --beyond-the-stars: #003657;
  --beyond-the-stars-rgb: 0 54 87;
  --beyond-the-stars-oklch: oklch(0.32 0.078 243.3);
}

.element {
  color: var(--beyond-the-stars);
  background-color: hsl(203 100% 17%);
  border-color: oklch(0.32 0.078 243.3);
}

Tailwind CSS v4

@theme {
  --color-beyond-the-stars: #003657;
  --color-beyond-the-stars-50: #e4f8ff;
  --color-beyond-the-stars-100: #d3ebff;
  --color-beyond-the-stars-200: #b9d8f4;
  --color-beyond-the-stars-300: #97bcdd;
  --color-beyond-the-stars-400: #76a4c9;
  --color-beyond-the-stars-500: #568cb6;
  --color-beyond-the-stars-600: #4a779a;
  --color-beyond-the-stars-700: #3b5f7b;
  --color-beyond-the-stars-800: #29465b;
  --color-beyond-the-stars-900: #1b3040;
  --color-beyond-the-stars-950: #0b1c29;
}

SCSS

$beyond-the-stars: #003657;
$beyond-the-stars-rgb: 0, 54, 87;
$beyond-the-stars-light: mix(#fff, $beyond-the-stars, 20%);
$beyond-the-stars-dark: mix(#000, $beyond-the-stars, 20%);

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