#557A88

CSS

:root {
  --night-owl: #557a88;
  --night-owl-rgb: 85 122 136;
  --night-owl-oklch: oklch(0.557 0.047 223.5);
}

.element {
  color: var(--night-owl);
  background-color: hsl(196 23% 43%);
  border-color: oklch(0.557 0.047 223.5);
}

Tailwind CSS v4

@theme {
  --color-night-owl: #557a88;
  --color-night-owl-50: #e8f8ff;
  --color-night-owl-100: #d8ecf4;
  --color-night-owl-200: #c0d9e4;
  --color-night-owl-300: #9fbdca;
  --color-night-owl-400: #81a5b3;
  --color-night-owl-500: #648d9d;
  --color-night-owl-600: #557885;
  --color-night-owl-700: #44606a;
  --color-night-owl-800: #30464e;
  --color-night-owl-900: #213136;
  --color-night-owl-950: #101d21;
}

SCSS

$night-owl: #557a88;
$night-owl-rgb: 85, 122, 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);
}