#1B739D

CSS

:root {
  --chill-of-the-night: #1b739d;
  --chill-of-the-night-rgb: 27 115 157;
  --chill-of-the-night-oklch: oklch(0.526 0.102 235.2);
}

.element {
  color: var(--chill-of-the-night);
  background-color: hsl(199 71% 36%);
  border-color: oklch(0.526 0.102 235.2);
}

Tailwind CSS v4

@theme {
  --color-chill-of-the-night: #1b739d;
  --color-chill-of-the-night-50: #dbfaff;
  --color-chill-of-the-night-100: #c9eeff;
  --color-chill-of-the-night-200: #abdcfb;
  --color-chill-of-the-night-300: #84c0e6;
  --color-chill-of-the-night-400: #5da8d2;
  --color-chill-of-the-night-500: #3190c0;
  --color-chill-of-the-night-600: #2c7aa2;
  --color-chill-of-the-night-700: #236282;
  --color-chill-of-the-night-800: #154860;
  --color-chill-of-the-night-900: #0e3243;
  --color-chill-of-the-night-950: #011e2b;
}

SCSS

$chill-of-the-night: #1b739d;
$chill-of-the-night-rgb: 27, 115, 157;
$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);
}