#D90131

CSS

:root {
  --rare-red: #d90131;
  --rare-red-rgb: 217 1 49;
  --rare-red-oklch: oklch(0.559 0.225 21.9);
}

.element {
  color: var(--rare-red);
  background-color: hsl(347 99% 43%);
  border-color: oklch(0.559 0.225 21.9);
}

Tailwind CSS v4

@theme {
  --color-rare-red: #d90131;
  --color-rare-red-50: #ffdcd6;
  --color-rare-red-100: #ffcac3;
  --color-rare-red-200: #ffaca5;
  --color-rare-red-300: #ff827d;
  --color-rare-red-400: #ff565f;
  --color-rare-red-500: #f8083a;
  --color-rare-red-600: #d11433;
  --color-rare-red-700: #a91228;
  --color-rare-red-800: #7e091f;
  --color-rare-red-900: #590714;
  --color-rare-red-950: #3c0006;
}

SCSS

$rare-red: #d90131;
$rare-red-rgb: 217, 1, 49;
$rare-red-light: mix(#fff, $rare-red, 20%);
$rare-red-dark: mix(#000, $rare-red, 20%);

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