#297398

CSS

:root {
  --chill-of-the-night: #297398;
  --chill-of-the-night-rgb: 41 115 152;
  --chill-of-the-night-oklch: oklch(0.527 0.092 234.4);
}

.element {
  color: var(--chill-of-the-night);
  background-color: hsl(200 58% 38%);
  border-color: oklch(0.527 0.092 234.4);
}

Tailwind CSS v4

@theme {
  --color-chill-of-the-night: #297398;
  --color-chill-of-the-night-50: #ddfaff;
  --color-chill-of-the-night-100: #ccedff;
  --color-chill-of-the-night-200: #afdbf7;
  --color-chill-of-the-night-300: #8abfe1;
  --color-chill-of-the-night-400: #65a8cd;
  --color-chill-of-the-night-500: #3e90ba;
  --color-chill-of-the-night-600: #367a9d;
  --color-chill-of-the-night-700: #2b617e;
  --color-chill-of-the-night-800: #1c485d;
  --color-chill-of-the-night-900: #123241;
  --color-chill-of-the-night-950: #041e2a;
}

SCSS

$chill-of-the-night: #297398;
$chill-of-the-night-rgb: 41, 115, 152;
$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);
}