#120D14

CSS

:root {
  --back-in-black: #120d14;
  --back-in-black-rgb: 18 13 20;
  --back-in-black-oklch: oklch(0.169 0.016 316.2);
}

.element {
  color: var(--back-in-black);
  background-color: hsl(283 21% 6%);
  border-color: oklch(0.169 0.016 316.2);
}

Tailwind CSS v4

@theme {
  --color-back-in-black: #120d14;
  --color-back-in-black-50: #f7f4f8;
  --color-back-in-black-100: #eae6eb;
  --color-back-in-black-200: #d7d2d9;
  --color-back-in-black-300: #bbb5bd;
  --color-back-in-black-400: #a29ca5;
  --color-back-in-black-500: #8b838e;
  --color-back-in-black-600: #756f78;
  --color-back-in-black-700: #5e5960;
  --color-back-in-black-800: #444146;
  --color-back-in-black-900: #2f2d31;
  --color-back-in-black-950: #1c1a1d;
}

SCSS

$back-in-black: #120d14;
$back-in-black-rgb: 18, 13, 20;
$back-in-black-light: mix(#fff, $back-in-black, 20%);
$back-in-black-dark: mix(#000, $back-in-black, 20%);

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