#171833

CSS

:root {
  --dark-knight: #171833;
  --dark-knight-rgb: 23 24 51;
  --dark-knight-oklch: oklch(0.224 0.052 279.7);
}

.element {
  color: var(--dark-knight);
  background-color: hsl(238 38% 15%);
  border-color: oklch(0.224 0.052 279.7);
}

Tailwind CSS v4

@theme {
  --color-dark-knight: #171833;
  --color-dark-knight-50: #f2f4ff;
  --color-dark-knight-100: #e4e6f9;
  --color-dark-knight-200: #d0d2eb;
  --color-dark-knight-300: #b2b5d2;
  --color-dark-knight-400: #989cbd;
  --color-dark-knight-500: #7f83a9;
  --color-dark-knight-600: #6b6f8e;
  --color-dark-knight-700: #565972;
  --color-dark-knight-800: #3e4154;
  --color-dark-knight-900: #2a2d3b;
  --color-dark-knight-950: #181a25;
}

SCSS

$dark-knight: #171833;
$dark-knight-rgb: 23, 24, 51;
$dark-knight-light: mix(#fff, $dark-knight, 20%);
$dark-knight-dark: mix(#000, $dark-knight, 20%);

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