#1C172B

CSS

:root {
  --dark-knight: #1c172b;
  --dark-knight-rgb: 28 23 43;
  --dark-knight-oklch: oklch(0.221 0.039 294.5);
}

.element {
  color: var(--dark-knight);
  background-color: hsl(255 30% 13%);
  border-color: oklch(0.221 0.039 294.5);
}

Tailwind CSS v4

@theme {
  --color-dark-knight: #1c172b;
  --color-dark-knight-50: #f6f3ff;
  --color-dark-knight-100: #e9e5f4;
  --color-dark-knight-200: #d5d1e3;
  --color-dark-knight-300: #b9b4c9;
  --color-dark-knight-400: #9f9ab4;
  --color-dark-knight-500: #87829e;
  --color-dark-knight-600: #736e85;
  --color-dark-knight-700: #5c586b;
  --color-dark-knight-800: #42404f;
  --color-dark-knight-900: #2e2c37;
  --color-dark-knight-950: #1b1922;
}

SCSS

$dark-knight: #1c172b;
$dark-knight-rgb: 28, 23, 43;
$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);
}