#003A3B

CSS

:root {
  --rich-black: #003a3b;
  --rich-black-rgb: 0 58 59;
  --rich-black-oklch: oklch(0.316 0.054 196.7);
}

.element {
  color: var(--rich-black);
  background-color: hsl(181 100% 12%);
  border-color: oklch(0.316 0.054 196.7);
}

Tailwind CSS v4

@theme {
  --color-rich-black: #003a3b;
  --color-rich-black-50: #e4fafb;
  --color-rich-black-100: #d4eeee;
  --color-rich-black-200: #bbdcdd;
  --color-rich-black-300: #98c0c2;
  --color-rich-black-400: #79a9a9;
  --color-rich-black-500: #599292;
  --color-rich-black-600: #4c7b7c;
  --color-rich-black-700: #3d6363;
  --color-rich-black-800: #2b4848;
  --color-rich-black-900: #1d3232;
  --color-rich-black-950: #0d1e1e;
}

SCSS

$rich-black: #003a3b;
$rich-black-rgb: 0, 58, 59;
$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);
}