#003082

CSS

:root {
  --below-the-surface: #003082;
  --below-the-surface-rgb: 0 48 130;
  --below-the-surface-oklch: oklch(0.342 0.146 260.8);
}

.element {
  color: var(--below-the-surface);
  background-color: hsl(218 100% 25%);
  border-color: oklch(0.342 0.146 260.8);
}

Tailwind CSS v4

@theme {
  --color-below-the-surface: #003082;
  --color-below-the-surface-50: #dff6ff;
  --color-below-the-surface-100: #cee9ff;
  --color-below-the-surface-200: #b3d5ff;
  --color-below-the-surface-300: #8fb7ff;
  --color-below-the-surface-400: #6b9df4;
  --color-below-the-surface-500: #4b83e6;
  --color-below-the-surface-600: #406fc2;
  --color-below-the-surface-700: #33599c;
  --color-below-the-surface-800: #214174;
  --color-below-the-surface-900: #152d52;
  --color-below-the-surface-950: #071a37;
}

SCSS

$below-the-surface: #003082;
$below-the-surface-rgb: 0, 48, 130;
$below-the-surface-light: mix(#fff, $below-the-surface, 20%);
$below-the-surface-dark: mix(#000, $below-the-surface, 20%);

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