#577266

CSS

:root {
  --dark-forest: #577266;
  --dark-forest-rgb: 87 114 102;
  --dark-forest-oklch: oklch(0.527 0.037 166);
}

.element {
  color: var(--dark-forest);
  background-color: hsl(153 13% 39%);
  border-color: oklch(0.527 0.037 166);
}

Tailwind CSS v4

@theme {
  --color-dark-forest: #577266;
  --color-dark-forest-50: #ecf9f3;
  --color-dark-forest-100: #ddece5;
  --color-dark-forest-200: #c6dad1;
  --color-dark-forest-300: #a6beb4;
  --color-dark-forest-400: #8ba699;
  --color-dark-forest-500: #708e81;
  --color-dark-forest-600: #5f786d;
  --color-dark-forest-700: #4b6057;
  --color-dark-forest-800: #37473f;
  --color-dark-forest-900: #25312b;
  --color-dark-forest-950: #141d19;
}

SCSS

$dark-forest: #577266;
$dark-forest-rgb: 87, 114, 102;
$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);
}