#0C2931

CSS

:root {
  --black-box: #0c2931;
  --black-box-rgb: 12 41 49;
  --black-box-oklch: oklch(0.263 0.037 219);
}

.element {
  color: var(--black-box);
  background-color: hsl(193 61% 12%);
  border-color: oklch(0.263 0.037 219);
}

Tailwind CSS v4

@theme {
  --color-black-box: #0c2931;
  --color-black-box-50: #eaf8fd;
  --color-black-box-100: #dbebf1;
  --color-black-box-200: #c4d8e0;
  --color-black-box-300: #a3bcc5;
  --color-black-box-400: #87a4ad;
  --color-black-box-500: #6b8c97;
  --color-black-box-600: #5b7780;
  --color-black-box-700: #485f66;
  --color-black-box-800: #34464b;
  --color-black-box-900: #233034;
  --color-black-box-950: #121c1f;
}

SCSS

$black-box: #0c2931;
$black-box-rgb: 12, 41, 49;
$black-box-light: mix(#fff, $black-box, 20%);
$black-box-dark: mix(#000, $black-box, 20%);

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