#587B8B

CSS

:root {
  --night-owl: #587b8b;
  --night-owl-rgb: 88 123 139;
  --night-owl-oklch: oklch(0.562 0.047 228);
}

.element {
  color: var(--night-owl);
  background-color: hsl(199 22% 45%);
  border-color: oklch(0.562 0.047 228);
}

Tailwind CSS v4

@theme {
  --color-night-owl: #587b8b;
  --color-night-owl-50: #e8f8ff;
  --color-night-owl-100: #d9ebf5;
  --color-night-owl-200: #c1d8e5;
  --color-night-owl-300: #a0bccb;
  --color-night-owl-400: #82a4b4;
  --color-night-owl-500: #658d9f;
  --color-night-owl-600: #567786;
  --color-night-owl-700: #455f6b;
  --color-night-owl-800: #31464f;
  --color-night-owl-900: #213037;
  --color-night-owl-950: #101d22;
}

SCSS

$night-owl: #587b8b;
$night-owl-rgb: 88, 123, 139;
$night-owl-light: mix(#fff, $night-owl, 20%);
$night-owl-dark: mix(#000, $night-owl, 20%);

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