#011C18

CSS

:root {
  --swamp-thing: #011c18;
  --swamp-thing-rgb: 1 28 24;
  --swamp-thing-oklch: oklch(0.204 0.035 181.8);
}

.element {
  color: var(--swamp-thing);
  background-color: hsl(171 93% 6%);
  border-color: oklch(0.204 0.035 181.8);
}

Tailwind CSS v4

@theme {
  --color-swamp-thing: #011c18;
  --color-swamp-thing-50: #ebf9f6;
  --color-swamp-thing-100: #dcece9;
  --color-swamp-thing-200: #c5d9d6;
  --color-swamp-thing-300: #a4beb9;
  --color-swamp-thing-400: #88a6a0;
  --color-swamp-thing-500: #6d8e88;
  --color-swamp-thing-600: #5c7873;
  --color-swamp-thing-700: #4a605c;
  --color-swamp-thing-800: #354743;
  --color-swamp-thing-900: #24312e;
  --color-swamp-thing-950: #131d1b;
}

SCSS

$swamp-thing: #011c18;
$swamp-thing-rgb: 1, 28, 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);
}