#23739A

CSS

:root {
  --chill-of-the-night: #23739a;
  --chill-of-the-night-rgb: 35 115 154;
  --chill-of-the-night-oklch: oklch(0.526 0.097 234.5);
}

.element {
  color: var(--chill-of-the-night);
  background-color: hsl(200 63% 37%);
  border-color: oklch(0.526 0.097 234.5);
}

Tailwind CSS v4

@theme {
  --color-chill-of-the-night: #23739a;
  --color-chill-of-the-night-50: #dcfaff;
  --color-chill-of-the-night-100: #caeeff;
  --color-chill-of-the-night-200: #aedbf9;
  --color-chill-of-the-night-300: #87c0e3;
  --color-chill-of-the-night-400: #61a8cf;
  --color-chill-of-the-night-500: #3890bc;
  --color-chill-of-the-night-600: #327a9f;
  --color-chill-of-the-night-700: #276280;
  --color-chill-of-the-night-800: #19485e;
  --color-chill-of-the-night-900: #103242;
  --color-chill-of-the-night-950: #031e2a;
}

SCSS

$chill-of-the-night: #23739a;
$chill-of-the-night-rgb: 35, 115, 154;
$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);
}