#637E5A

CSS

:root {
  --emerald-city: #637e5a;
  --emerald-city-rgb: 99 126 90;
  --emerald-city-oklch: oklch(0.562 0.062 138);
}

.element {
  color: var(--emerald-city);
  background-color: hsl(105 17% 42%);
  border-color: oklch(0.562 0.062 138);
}

Tailwind CSS v4

@theme {
  --color-emerald-city: #637e5a;
  --color-emerald-city-50: #ecfae9;
  --color-emerald-city-100: #ddedda;
  --color-emerald-city-200: #c7dbc2;
  --color-emerald-city-300: #a7c0a2;
  --color-emerald-city-400: #8da884;
  --color-emerald-city-500: #729068;
  --color-emerald-city-600: #617a58;
  --color-emerald-city-700: #4d6246;
  --color-emerald-city-800: #394732;
  --color-emerald-city-900: #273222;
  --color-emerald-city-950: #151d11;
}

SCSS

$emerald-city: #637e5a;
$emerald-city-rgb: 99, 126, 90;
$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);
}