#297397

CSS

:root {
  --chill-of-the-night: #297397;
  --chill-of-the-night-rgb: 41 115 151;
  --chill-of-the-night-oklch: oklch(0.526 0.091 233.6);
}

.element {
  color: var(--chill-of-the-night);
  background-color: hsl(200 57% 38%);
  border-color: oklch(0.526 0.091 233.6);
}

Tailwind CSS v4

@theme {
  --color-chill-of-the-night: #297397;
  --color-chill-of-the-night-50: #ddfaff;
  --color-chill-of-the-night-100: #ccedff;
  --color-chill-of-the-night-200: #afdbf6;
  --color-chill-of-the-night-300: #8abfe0;
  --color-chill-of-the-night-400: #65a8cc;
  --color-chill-of-the-night-500: #3e90b9;
  --color-chill-of-the-night-600: #367a9c;
  --color-chill-of-the-night-700: #2b617d;
  --color-chill-of-the-night-800: #1c485c;
  --color-chill-of-the-night-900: #123241;
  --color-chill-of-the-night-950: #041e29;
}

SCSS

$chill-of-the-night: #297397;
$chill-of-the-night-rgb: 41, 115, 151;
$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);
}