#000511

CSS

:root {
  --dark-rift: #000511;
  --dark-rift-rgb: 0 5 17;
  --dark-rift-oklch: oklch(0.115 0.035 252.4);
}

.element {
  color: var(--dark-rift);
  background-color: hsl(222 100% 3%);
  border-color: oklch(0.115 0.035 252.4);
}

Tailwind CSS v4

@theme {
  --color-dark-rift: #000511;
  --color-dark-rift-50: #eff6ff;
  --color-dark-rift-100: #e0e9f4;
  --color-dark-rift-200: #cad5e3;
  --color-dark-rift-300: #acb9c9;
  --color-dark-rift-400: #90a0b3;
  --color-dark-rift-500: #76889d;
  --color-dark-rift-600: #647385;
  --color-dark-rift-700: #505c6a;
  --color-dark-rift-800: #3a434e;
  --color-dark-rift-900: #272f36;
  --color-dark-rift-950: #161b21;
}

SCSS

$dark-rift: #000511;
$dark-rift-rgb: 0, 5, 17;
$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);
}