#00212A

CSS

:root {
  --black-box: #00212a;
  --black-box-rgb: 0 33 42;
  --black-box-oklch: oklch(0.229 0.042 219.6);
}

.element {
  color: var(--black-box);
  background-color: hsl(193 100% 8%);
  border-color: oklch(0.229 0.042 219.6);
}

Tailwind CSS v4

@theme {
  --color-black-box: #00212a;
  --color-black-box-50: #e9f8fe;
  --color-black-box-100: #daebf2;
  --color-black-box-200: #c2d9e1;
  --color-black-box-300: #a1bdc7;
  --color-black-box-400: #84a5af;
  --color-black-box-500: #678d99;
  --color-black-box-600: #587782;
  --color-black-box-700: #466068;
  --color-black-box-800: #32464c;
  --color-black-box-900: #223135;
  --color-black-box-950: #111d20;
}

SCSS

$black-box: #00212a;
$black-box-rgb: 0, 33, 42;
$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);
}