#5B7169

CSS

:root {
  --dark-forest: #5b7169;
  --dark-forest-rgb: 91 113 105;
  --dark-forest-oklch: oklch(0.528 0.029 171.1);
}

.element {
  color: var(--dark-forest);
  background-color: hsl(158 11% 40%);
  border-color: oklch(0.528 0.029 171.1);
}

Tailwind CSS v4

@theme {
  --color-dark-forest: #5b7169;
  --color-dark-forest-50: #edf8f4;
  --color-dark-forest-100: #dfebe7;
  --color-dark-forest-200: #c8d8d3;
  --color-dark-forest-300: #a9bcb6;
  --color-dark-forest-400: #8ea49c;
  --color-dark-forest-500: #748d84;
  --color-dark-forest-600: #62776f;
  --color-dark-forest-700: #4e5f59;
  --color-dark-forest-800: #394641;
  --color-dark-forest-900: #27302d;
  --color-dark-forest-950: #151c1a;
}

SCSS

$dark-forest: #5b7169;
$dark-forest-rgb: 91, 113, 105;
$dark-forest-light: mix(#fff, $dark-forest, 20%);
$dark-forest-dark: mix(#000, $dark-forest, 20%);

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