#004443

CSS

:root {
  --rich-black: #004443;
  --rich-black-rgb: 0 68 67;
  --rich-black-oklch: oklch(0.35 0.06 193.1);
}

.element {
  color: var(--rich-black);
  background-color: hsl(179 100% 13%);
  border-color: oklch(0.35 0.06 193.1);
}

Tailwind CSS v4

@theme {
  --color-rich-black: #004443;
  --color-rich-black-50: #e3fbfa;
  --color-rich-black-100: #d2efee;
  --color-rich-black-200: #b8dddc;
  --color-rich-black-300: #94c1c1;
  --color-rich-black-400: #74aaa8;
  --color-rich-black-500: #539391;
  --color-rich-black-600: #477c7b;
  --color-rich-black-700: #396462;
  --color-rich-black-800: #284947;
  --color-rich-black-900: #1b3331;
  --color-rich-black-950: #0b1e1d;
}

SCSS

$rich-black: #004443;
$rich-black-rgb: 0, 68, 67;
$rich-black-light: mix(#fff, $rich-black, 20%);
$rich-black-dark: mix(#000, $rich-black, 20%);

.element {
  color: $rich-black;
  box-shadow: 0 0 0 2px rgba($rich-black, 0.35);
}