#9E0000

CSS

:root {
  --cacodemon-red: #9e0000;
  --cacodemon-red-rgb: 158 0 0;
  --cacodemon-red-oklch: oklch(0.439 0.18 29.2);
}

.element {
  color: var(--cacodemon-red);
  background-color: hsl(0 100% 31%);
  border-color: oklch(0.439 0.18 29.2);
}

Tailwind CSS v4

@theme {
  --color-cacodemon-red: #9e0000;
  --color-cacodemon-red-50: #ffe3d6;
  --color-cacodemon-red-100: #ffd2c3;
  --color-cacodemon-red-200: #ffb7a5;
  --color-cacodemon-red-300: #ff927d;
  --color-cacodemon-red-400: #f66e5d;
  --color-cacodemon-red-500: #e54637;
  --color-cacodemon-red-600: #c13d30;
  --color-cacodemon-red-700: #9b3026;
  --color-cacodemon-red-800: #74211d;
  --color-cacodemon-red-900: #521613;
  --color-cacodemon-red-950: #360605;
}

SCSS

$cacodemon-red: #9e0000;
$cacodemon-red-rgb: 158, 0, 0;
$cacodemon-red-light: mix(#fff, $cacodemon-red, 20%);
$cacodemon-red-dark: mix(#000, $cacodemon-red, 20%);

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