#3F3F3F

CSS

:root {
  --black-panther: #3f3f3f;
  --black-panther-rgb: 63 63 63;
  --black-panther-oklch: oklch(0.368 0 0);
}

.element {
  color: var(--black-panther);
  background-color: hsl(0 0% 25%);
  border-color: oklch(0.368 0 0);
}

Tailwind CSS v4

@theme {
  --color-black-panther: #3f3f3f;
  --color-black-panther-50: #f5f5f5;
  --color-black-panther-100: #e8e8e8;
  --color-black-panther-200: #d4d4d4;
  --color-black-panther-300: #b7b7b7;
  --color-black-panther-400: #9e9e9e;
  --color-black-panther-500: #868686;
  --color-black-panther-600: #717171;
  --color-black-panther-700: #5b5b5b;
  --color-black-panther-800: #424242;
  --color-black-panther-900: #2e2e2e;
  --color-black-panther-950: #1b1b1b;
}

SCSS

$black-panther: #3f3f3f;
$black-panther-rgb: 63, 63, 63;
$black-panther-light: mix(#fff, $black-panther, 20%);
$black-panther-dark: mix(#000, $black-panther, 20%);

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