#287399

CSS

:root {
  --chill-of-the-night: #287399;
  --chill-of-the-night-rgb: 40 115 153;
  --chill-of-the-night-oklch: oklch(0.527 0.094 234.8);
}

.element {
  color: var(--chill-of-the-night);
  background-color: hsl(200 59% 38%);
  border-color: oklch(0.527 0.094 234.8);
}

Tailwind CSS v4

@theme {
  --color-chill-of-the-night: #287399;
  --color-chill-of-the-night-50: #ddfaff;
  --color-chill-of-the-night-100: #cbedff;
  --color-chill-of-the-night-200: #afdbf8;
  --color-chill-of-the-night-300: #89bfe2;
  --color-chill-of-the-night-400: #64a8ce;
  --color-chill-of-the-night-500: #3d90bb;
  --color-chill-of-the-night-600: #357a9e;
  --color-chill-of-the-night-700: #2a617f;
  --color-chill-of-the-night-800: #1b485d;
  --color-chill-of-the-night-900: #123241;
  --color-chill-of-the-night-950: #041d2a;
}

SCSS

$chill-of-the-night: #287399;
$chill-of-the-night-rgb: 40, 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);
}