#646998

CSS

:root {
  --twinkle-night: #646998;
  --twinkle-night-rgb: 100 105 152;
  --twinkle-night-oklch: oklch(0.536 0.074 278.9);
}

.element {
  color: var(--twinkle-night);
  background-color: hsl(234 21% 49%);
  border-color: oklch(0.536 0.074 278.9);
}

Tailwind CSS v4

@theme {
  --color-twinkle-night: #646998;
  --color-twinkle-night-50: #f1f3ff;
  --color-twinkle-night-100: #e3e6ff;
  --color-twinkle-night-200: #ced1f4;
  --color-twinkle-night-300: #b0b4dd;
  --color-twinkle-night-400: #949aca;
  --color-twinkle-night-500: #7b81b7;
  --color-twinkle-night-600: #686d9a;
  --color-twinkle-night-700: #53577c;
  --color-twinkle-night-800: #3c405c;
  --color-twinkle-night-900: #292c40;
  --color-twinkle-night-950: #171929;
}

SCSS

$twinkle-night: #646998;
$twinkle-night-rgb: 100, 105, 152;
$twinkle-night-light: mix(#fff, $twinkle-night, 20%);
$twinkle-night-dark: mix(#000, $twinkle-night, 20%);

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