#002A78

CSS

:root {
  --below-the-surface: #002a78;
  --below-the-surface-rgb: 0 42 120;
  --below-the-surface-oklch: oklch(0.319 0.14 261.3);
}

.element {
  color: var(--below-the-surface);
  background-color: hsl(219 100% 24%);
  border-color: oklch(0.319 0.14 261.3);
}

Tailwind CSS v4

@theme {
  --color-below-the-surface: #002a78;
  --color-below-the-surface-50: #e0f6ff;
  --color-below-the-surface-100: #d0e9ff;
  --color-below-the-surface-200: #b5d5ff;
  --color-below-the-surface-300: #92b7ff;
  --color-below-the-surface-400: #6f9df1;
  --color-below-the-surface-500: #4f83e2;
  --color-below-the-surface-600: #436fbe;
  --color-below-the-surface-700: #355999;
  --color-below-the-surface-800: #234272;
  --color-below-the-surface-900: #172d50;
  --color-below-the-surface-950: #081a36;
}

SCSS

$below-the-surface: #002a78;
$below-the-surface-rgb: 0, 42, 120;
$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);
}