#2A293A

CSS

:root {
  --black-velvet: #2a293a;
  --black-velvet-rgb: 42 41 58;
  --black-velvet-oklch: oklch(0.29 0.031 287);
}

.element {
  color: var(--black-velvet);
  background-color: hsl(244 17% 19%);
  border-color: oklch(0.29 0.031 287);
}

Tailwind CSS v4

@theme {
  --color-black-velvet: #2a293a;
  --color-black-velvet-50: #f4f4fe;
  --color-black-velvet-100: #e7e6f2;
  --color-black-velvet-200: #d3d2e1;
  --color-black-velvet-300: #b6b5c7;
  --color-black-velvet-400: #9d9cb0;
  --color-black-velvet-500: #84839a;
  --color-black-velvet-600: #706f82;
  --color-black-velvet-700: #595968;
  --color-black-velvet-800: #41414d;
  --color-black-velvet-900: #2d2d35;
  --color-black-velvet-950: #1a1a21;
}

SCSS

$black-velvet: #2a293a;
$black-velvet-rgb: 42, 41, 58;
$black-velvet-light: mix(#fff, $black-velvet, 20%);
$black-velvet-dark: mix(#000, $black-velvet, 20%);

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