#647B5B

CSS

:root {
  --emerald-city: #647b5b;
  --emerald-city-rgb: 100 123 91;
  --emerald-city-oklch: oklch(0.555 0.055 137);
}

.element {
  color: var(--emerald-city);
  background-color: hsl(103 15% 42%);
  border-color: oklch(0.555 0.055 137);
}

Tailwind CSS v4

@theme {
  --color-emerald-city: #647b5b;
  --color-emerald-city-50: #edf9ea;
  --color-emerald-city-100: #dfeddb;
  --color-emerald-city-200: #c9dac4;
  --color-emerald-city-300: #a9bfa4;
  --color-emerald-city-400: #8fa686;
  --color-emerald-city-500: #758f6b;
  --color-emerald-city-600: #63795b;
  --color-emerald-city-700: #4f6148;
  --color-emerald-city-800: #3a4734;
  --color-emerald-city-900: #283123;
  --color-emerald-city-950: #161d12;
}

SCSS

$emerald-city: #647b5b;
$emerald-city-rgb: 100, 123, 91;
$emerald-city-light: mix(#fff, $emerald-city, 20%);
$emerald-city-dark: mix(#000, $emerald-city, 20%);

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