#031019

CSS

:root {
  --black-knight: #031019;
  --black-knight-rgb: 3 16 25;
  --black-knight-oklch: oklch(0.165 0.028 237.5);
}

.element {
  color: var(--black-knight);
  background-color: hsl(205 79% 5%);
  border-color: oklch(0.165 0.028 237.5);
}

Tailwind CSS v4

@theme {
  --color-black-knight: #031019;
  --color-black-knight-50: #eef6fd;
  --color-black-knight-100: #e0e9f0;
  --color-black-knight-200: #cad6df;
  --color-black-knight-300: #abbac5;
  --color-black-knight-400: #90a1ad;
  --color-black-knight-500: #758997;
  --color-black-knight-600: #637480;
  --color-black-knight-700: #4f5d66;
  --color-black-knight-800: #39444b;
  --color-black-knight-900: #272f34;
  --color-black-knight-950: #151c1f;
}

SCSS

$black-knight: #031019;
$black-knight-rgb: 3, 16, 25;
$black-knight-light: mix(#fff, $black-knight, 20%);
$black-knight-dark: mix(#000, $black-knight, 20%);

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