#003435

CSS

:root {
  --rich-black: #003435;
  --rich-black-rgb: 0 52 53;
  --rich-black-oklch: oklch(0.295 0.05 196.9);
}

.element {
  color: var(--rich-black);
  background-color: hsl(181 100% 10%);
  border-color: oklch(0.295 0.05 196.9);
}

Tailwind CSS v4

@theme {
  --color-rich-black: #003435;
  --color-rich-black-50: #e6fafa;
  --color-rich-black-100: #d6edee;
  --color-rich-black-200: #bcdbdc;
  --color-rich-black-300: #9ac0c1;
  --color-rich-black-400: #7ca8a8;
  --color-rich-black-500: #5d9191;
  --color-rich-black-600: #4f7a7b;
  --color-rich-black-700: #3f6262;
  --color-rich-black-800: #2d4848;
  --color-rich-black-900: #1e3232;
  --color-rich-black-950: #0e1e1e;
}

SCSS

$rich-black: #003435;
$rich-black-rgb: 0, 52, 53;
$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);
}