#51689D

CSS

:root {
  --starstruck: #51689d;
  --starstruck-rgb: 81 104 157;
  --starstruck-oklch: oklch(0.522 0.089 265.6);
}

.element {
  color: var(--starstruck);
  background-color: hsl(222 32% 47%);
  border-color: oklch(0.522 0.089 265.6);
}

Tailwind CSS v4

@theme {
  --color-starstruck: #51689d;
  --color-starstruck-50: #eaf5ff;
  --color-starstruck-100: #dbe8ff;
  --color-starstruck-200: #c4d4fb;
  --color-starstruck-300: #a3b7e6;
  --color-starstruck-400: #859ed4;
  --color-starstruck-500: #6a85c1;
  --color-starstruck-600: #5a70a3;
  --color-starstruck-700: #485a83;
  --color-starstruck-800: #324261;
  --color-starstruck-900: #222e44;
  --color-starstruck-950: #111a2c;
}

SCSS

$starstruck: #51689d;
$starstruck-rgb: 81, 104, 157;
$starstruck-light: mix(#fff, $starstruck, 20%);
$starstruck-dark: mix(#000, $starstruck, 20%);

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