#101631

CSS

:root {
  --dark-knight: #101631;
  --dark-knight-rgb: 16 22 49;
  --dark-knight-oklch: oklch(0.211 0.054 271.7);
}

.element {
  color: var(--dark-knight);
  background-color: hsl(229 51% 13%);
  border-color: oklch(0.211 0.054 271.7);
}

Tailwind CSS v4

@theme {
  --color-dark-knight: #101631;
  --color-dark-knight-50: #f0f4ff;
  --color-dark-knight-100: #e2e7fb;
  --color-dark-knight-200: #cdd3ec;
  --color-dark-knight-300: #aeb6d4;
  --color-dark-knight-400: #939dbf;
  --color-dark-knight-500: #7985ab;
  --color-dark-knight-600: #677090;
  --color-dark-knight-700: #525a74;
  --color-dark-knight-800: #3b4255;
  --color-dark-knight-900: #282d3c;
  --color-dark-knight-950: #161a25;
}

SCSS

$dark-knight: #101631;
$dark-knight-rgb: 16, 22, 49;
$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);
}