#002F7B

CSS

:root {
  --below-the-surface: #002f7b;
  --below-the-surface-rgb: 0 47 123;
  --below-the-surface-oklch: oklch(0.333 0.138 260.3);
}

.element {
  color: var(--below-the-surface);
  background-color: hsl(217 100% 24%);
  border-color: oklch(0.333 0.138 260.3);
}

Tailwind CSS v4

@theme {
  --color-below-the-surface: #002f7b;
  --color-below-the-surface-50: #e0f6ff;
  --color-below-the-surface-100: #cfe9ff;
  --color-below-the-surface-200: #b5d5ff;
  --color-below-the-surface-300: #91b7fe;
  --color-below-the-surface-400: #6e9eef;
  --color-below-the-surface-500: #4d84e0;
  --color-below-the-surface-600: #4270bd;
  --color-below-the-surface-700: #345998;
  --color-below-the-surface-800: #224271;
  --color-below-the-surface-900: #172e50;
  --color-below-the-surface-950: #081a35;
}

SCSS

$below-the-surface: #002f7b;
$below-the-surface-rgb: 0, 47, 123;
$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);
}