#287395

CSS

:root {
  --chill-of-the-night: #287395;
  --chill-of-the-night-rgb: 40 115 149;
  --chill-of-the-night-oklch: oklch(0.525 0.09 231.9);
}

.element {
  color: var(--chill-of-the-night);
  background-color: hsl(199 58% 37%);
  border-color: oklch(0.525 0.09 231.9);
}

Tailwind CSS v4

@theme {
  --color-chill-of-the-night: #287395;
  --color-chill-of-the-night-50: #ddfaff;
  --color-chill-of-the-night-100: #cceeff;
  --color-chill-of-the-night-200: #afdbf5;
  --color-chill-of-the-night-300: #89c0df;
  --color-chill-of-the-night-400: #64a8ca;
  --color-chill-of-the-night-500: #3e90b7;
  --color-chill-of-the-night-600: #367a9b;
  --color-chill-of-the-night-700: #2b627c;
  --color-chill-of-the-night-800: #1c485b;
  --color-chill-of-the-night-900: #123240;
  --color-chill-of-the-night-950: #041e29;
}

SCSS

$chill-of-the-night: #287395;
$chill-of-the-night-rgb: 40, 115, 149;
$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);
}