#002220

CSS

:root {
  --swamp-thing: #002220;
  --swamp-thing-rgb: 0 34 32;
  --swamp-thing-oklch: oklch(0.227 0.039 189.1);
}

.element {
  color: var(--swamp-thing);
  background-color: hsl(176 100% 7%);
  border-color: oklch(0.227 0.039 189.1);
}

Tailwind CSS v4

@theme {
  --color-swamp-thing: #002220;
  --color-swamp-thing-50: #e9f9f8;
  --color-swamp-thing-100: #daeceb;
  --color-swamp-thing-200: #c2dad8;
  --color-swamp-thing-300: #a1bebc;
  --color-swamp-thing-400: #85a6a3;
  --color-swamp-thing-500: #688f8b;
  --color-swamp-thing-600: #587976;
  --color-swamp-thing-700: #47615e;
  --color-swamp-thing-800: #334745;
  --color-swamp-thing-900: #23312f;
  --color-swamp-thing-950: #121d1c;
}

SCSS

$swamp-thing: #002220;
$swamp-thing-rgb: 0, 34, 32;
$swamp-thing-light: mix(#fff, $swamp-thing, 20%);
$swamp-thing-dark: mix(#000, $swamp-thing, 20%);

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