#003F46

CSS

:root {
  --rich-black: #003f46;
  --rich-black-rgb: 0 63 70;
  --rich-black-oklch: oklch(0.336 0.058 207.2);
}

.element {
  color: var(--rich-black);
  background-color: hsl(186 100% 14%);
  border-color: oklch(0.336 0.058 207.2);
}

Tailwind CSS v4

@theme {
  --color-rich-black: #003f46;
  --color-rich-black-50: #e3fafe;
  --color-rich-black-100: #d3eef2;
  --color-rich-black-200: #b9dce2;
  --color-rich-black-300: #96c0c7;
  --color-rich-black-400: #76a9b0;
  --color-rich-black-500: #55919a;
  --color-rich-black-600: #497b82;
  --color-rich-black-700: #3a6268;
  --color-rich-black-800: #29484c;
  --color-rich-black-900: #1c3235;
  --color-rich-black-950: #0c1e20;
}

SCSS

$rich-black: #003f46;
$rich-black-rgb: 0, 63, 70;
$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);
}