#10172B

CSS

:root {
  --sombre-night: #10172b;
  --sombre-night-rgb: 16 23 43;
  --sombre-night-oklch: oklch(0.209 0.041 268.1);
}

.element {
  color: var(--sombre-night);
  background-color: hsl(224 46% 12%);
  border-color: oklch(0.209 0.041 268.1);
}

Tailwind CSS v4

@theme {
  --color-sombre-night: #10172b;
  --color-sombre-night-50: #f0f5ff;
  --color-sombre-night-100: #e2e8f6;
  --color-sombre-night-200: #cdd4e7;
  --color-sombre-night-300: #afb7cd;
  --color-sombre-night-400: #949eb8;
  --color-sombre-night-500: #7a86a2;
  --color-sombre-night-600: #687189;
  --color-sombre-night-700: #535a6e;
  --color-sombre-night-800: #3c4251;
  --color-sombre-night-900: #292e38;
  --color-sombre-night-950: #171b23;
}

SCSS

$sombre-night: #10172b;
$sombre-night-rgb: 16, 23, 43;
$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);
}