#5B716B

CSS

:root {
  --dark-forest: #5b716b;
  --dark-forest-rgb: 91 113 107;
  --dark-forest-oklch: oklch(0.529 0.028 176.8);
}

.element {
  color: var(--dark-forest);
  background-color: hsl(164 11% 40%);
  border-color: oklch(0.529 0.028 176.8);
}

Tailwind CSS v4

@theme {
  --color-dark-forest: #5b716b;
  --color-dark-forest-50: #edf8f5;
  --color-dark-forest-100: #dfebe8;
  --color-dark-forest-200: #c8d8d4;
  --color-dark-forest-300: #a9bcb7;
  --color-dark-forest-400: #8ea49e;
  --color-dark-forest-500: #738c86;
  --color-dark-forest-600: #627771;
  --color-dark-forest-700: #4e5f5a;
  --color-dark-forest-800: #394642;
  --color-dark-forest-900: #27302d;
  --color-dark-forest-950: #151c1a;
}

SCSS

$dark-forest: #5b716b;
$dark-forest-rgb: 91, 113, 107;
$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);
}