#001B18

CSS

:root {
  --swamp-thing: #001b18;
  --swamp-thing-rgb: 0 27 24;
  --swamp-thing-oklch: oklch(0.2 0.035 185);
}

.element {
  color: var(--swamp-thing);
  background-color: hsl(173 100% 5%);
  border-color: oklch(0.2 0.035 185);
}

Tailwind CSS v4

@theme {
  --color-swamp-thing: #001b18;
  --color-swamp-thing-50: #ebf9f7;
  --color-swamp-thing-100: #dcecea;
  --color-swamp-thing-200: #c4d9d7;
  --color-swamp-thing-300: #a4beba;
  --color-swamp-thing-400: #88a6a1;
  --color-swamp-thing-500: #6c8e89;
  --color-swamp-thing-600: #5c7874;
  --color-swamp-thing-700: #49605d;
  --color-swamp-thing-800: #354743;
  --color-swamp-thing-900: #24312f;
  --color-swamp-thing-950: #131d1b;
}

SCSS

$swamp-thing: #001b18;
$swamp-thing-rgb: 0, 27, 24;
$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);
}