#0D1A32

CSS

:root {
  --sombre-night: #0d1a32;
  --sombre-night-rgb: 13 26 50;
  --sombre-night-oklch: oklch(0.22 0.051 261.7);
}

.element {
  color: var(--sombre-night);
  background-color: hsl(219 59% 12%);
  border-color: oklch(0.22 0.051 261.7);
}

Tailwind CSS v4

@theme {
  --color-sombre-night: #0d1a32;
  --color-sombre-night-50: #eef5ff;
  --color-sombre-night-100: #dfe8f9;
  --color-sombre-night-200: #c9d5eb;
  --color-sombre-night-300: #aab8d2;
  --color-sombre-night-400: #8e9fbd;
  --color-sombre-night-500: #7487a8;
  --color-sombre-night-600: #62728e;
  --color-sombre-night-700: #4e5b72;
  --color-sombre-night-800: #384354;
  --color-sombre-night-900: #262e3b;
  --color-sombre-night-950: #151b25;
}

SCSS

$sombre-night: #0d1a32;
$sombre-night-rgb: 13, 26, 50;
$sombre-night-light: mix(#fff, $sombre-night, 20%);
$sombre-night-dark: mix(#000, $sombre-night, 20%);

.element {
  color: $sombre-night;
  box-shadow: 0 0 0 2px rgba($sombre-night, 0.35);
}