#002D75

CSS

:root {
  --below-the-surface: #002d75;
  --below-the-surface-rgb: 0 45 117;
  --below-the-surface-oklch: oklch(0.322 0.132 260.1);
}

.element {
  color: var(--below-the-surface);
  background-color: hsl(217 100% 23%);
  border-color: oklch(0.322 0.132 260.1);
}

Tailwind CSS v4

@theme {
  --color-below-the-surface: #002d75;
  --color-below-the-surface-50: #e1f6ff;
  --color-below-the-surface-100: #d0e9ff;
  --color-below-the-surface-200: #b6d5ff;
  --color-below-the-surface-300: #92b8fb;
  --color-below-the-surface-400: #709eec;
  --color-below-the-surface-500: #5084dd;
  --color-below-the-surface-600: #4470ba;
  --color-below-the-surface-700: #365a95;
  --color-below-the-surface-800: #24426f;
  --color-below-the-surface-900: #182e4e;
  --color-below-the-surface-950: #091a34;
}

SCSS

$below-the-surface: #002d75;
$below-the-surface-rgb: 0, 45, 117;
$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);
}