#5B7B88

CSS

:root {
  --night-owl: #5b7b88;
  --night-owl-rgb: 91 123 136;
  --night-owl-oklch: oklch(0.563 0.042 224.9);
}

.element {
  color: var(--night-owl);
  background-color: hsl(197 20% 45%);
  border-color: oklch(0.563 0.042 224.9);
}

Tailwind CSS v4

@theme {
  --color-night-owl: #5b7b88;
  --color-night-owl-50: #e9f8ff;
  --color-night-owl-100: #daebf3;
  --color-night-owl-200: #c3d8e2;
  --color-night-owl-300: #a2bcc8;
  --color-night-owl-400: #85a4b1;
  --color-night-owl-500: #688c9b;
  --color-night-owl-600: #597783;
  --color-night-owl-700: #475f69;
  --color-night-owl-800: #33464d;
  --color-night-owl-900: #223035;
  --color-night-owl-950: #111d21;
}

SCSS

$night-owl: #5b7b88;
$night-owl-rgb: 91, 123, 136;
$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);
}