#0F172D

CSS

:root {
  --dark-knight: #0f172d;
  --dark-knight-rgb: 15 23 45;
  --dark-knight-oklch: oklch(0.21 0.045 267.4);
}

.element {
  color: var(--dark-knight);
  background-color: hsl(224 50% 12%);
  border-color: oklch(0.21 0.045 267.4);
}

Tailwind CSS v4

@theme {
  --color-dark-knight: #0f172d;
  --color-dark-knight-50: #f0f5ff;
  --color-dark-knight-100: #e2e8f8;
  --color-dark-knight-200: #ccd4e8;
  --color-dark-knight-300: #aeb7cf;
  --color-dark-knight-400: #929eba;
  --color-dark-knight-500: #7986a5;
  --color-dark-knight-600: #66718b;
  --color-dark-knight-700: #525b70;
  --color-dark-knight-800: #3b4252;
  --color-dark-knight-900: #282e39;
  --color-dark-knight-950: #161b24;
}

SCSS

$dark-knight: #0f172d;
$dark-knight-rgb: 15, 23, 45;
$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);
}