#0D1117

CSS

:root {
  --dark-rift: #0d1117;
  --dark-rift-rgb: 13 17 23;
  --dark-rift-oklch: oklch(0.176 0.014 258.4);
}

.element {
  color: var(--dark-rift);
  background-color: hsl(216 28% 7%);
  border-color: oklch(0.176 0.014 258.4);
}

Tailwind CSS v4

@theme {
  --color-dark-rift: #0d1117;
  --color-dark-rift-50: #f3f5f9;
  --color-dark-rift-100: #e5e8ed;
  --color-dark-rift-200: #d1d4da;
  --color-dark-rift-300: #b3b8bf;
  --color-dark-rift-400: #999fa7;
  --color-dark-rift-500: #818790;
  --color-dark-rift-600: #6d727a;
  --color-dark-rift-700: #575b61;
  --color-dark-rift-800: #3f4347;
  --color-dark-rift-900: #2c2e31;
  --color-dark-rift-950: #191b1d;
}

SCSS

$dark-rift: #0d1117;
$dark-rift-rgb: 13, 17, 23;
$dark-rift-light: mix(#fff, $dark-rift, 20%);
$dark-rift-dark: mix(#000, $dark-rift, 20%);

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