#0F2135

CSS

:root {
  --the-count-s-black: #0f2135;
  --the-count-s-black-rgb: 15 33 53;
  --the-count-s-black-oklch: oklch(0.243 0.045 252.4);
}

.element {
  color: var(--the-count-s-black);
  background-color: hsl(212 56% 13%);
  border-color: oklch(0.243 0.045 252.4);
}

Tailwind CSS v4

@theme {
  --color-the-count-s-black: #0f2135;
  --color-the-count-s-black-50: #edf6ff;
  --color-the-count-s-black-100: #dee9f7;
  --color-the-count-s-black-200: #c7d6e8;
  --color-the-count-s-black-300: #a8b9cf;
  --color-the-count-s-black-400: #8ca1b9;
  --color-the-count-s-black-500: #7189a4;
  --color-the-count-s-black-600: #60748b;
  --color-the-count-s-black-700: #4c5c6f;
  --color-the-count-s-black-800: #374452;
  --color-the-count-s-black-900: #252f39;
  --color-the-count-s-black-950: #141b23;
}

SCSS

$the-count-s-black: #0f2135;
$the-count-s-black-rgb: 15, 33, 53;
$the-count-s-black-light: mix(#fff, $the-count-s-black, 20%);
$the-count-s-black-dark: mix(#000, $the-count-s-black, 20%);

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