#247399

CSS

:root {
  --chill-of-the-night: #247399;
  --chill-of-the-night-rgb: 36 115 153;
  --chill-of-the-night-oklch: oklch(0.526 0.095 234);
}

.element {
  color: var(--chill-of-the-night);
  background-color: hsl(199 62% 37%);
  border-color: oklch(0.526 0.095 234);
}

Tailwind CSS v4

@theme {
  --color-chill-of-the-night: #247399;
  --color-chill-of-the-night-50: #dcfaff;
  --color-chill-of-the-night-100: #cbeeff;
  --color-chill-of-the-night-200: #aedbf8;
  --color-chill-of-the-night-300: #88c0e2;
  --color-chill-of-the-night-400: #62a8ce;
  --color-chill-of-the-night-500: #3990bb;
  --color-chill-of-the-night-600: #327a9e;
  --color-chill-of-the-night-700: #28627f;
  --color-chill-of-the-night-800: #1a485e;
  --color-chill-of-the-night-900: #113242;
  --color-chill-of-the-night-950: #031e2a;
}

SCSS

$chill-of-the-night: #247399;
$chill-of-the-night-rgb: 36, 115, 153;
$chill-of-the-night-light: mix(#fff, $chill-of-the-night, 20%);
$chill-of-the-night-dark: mix(#000, $chill-of-the-night, 20%);

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