#2E3450

CSS

:root {
  --mediaeval-blue: #2e3450;
  --mediaeval-blue-rgb: 46 52 80;
  --mediaeval-blue-oklch: oklch(0.333 0.05 274.1);
}

.element {
  color: var(--mediaeval-blue);
  background-color: hsl(229 27% 25%);
  border-color: oklch(0.333 0.05 274.1);
}

Tailwind CSS v4

@theme {
  --color-mediaeval-blue: #2e3450;
  --color-mediaeval-blue-50: #f1f4ff;
  --color-mediaeval-blue-100: #e3e7f9;
  --color-mediaeval-blue-200: #ced3ea;
  --color-mediaeval-blue-300: #b0b6d2;
  --color-mediaeval-blue-400: #959dbd;
  --color-mediaeval-blue-500: #7c84a8;
  --color-mediaeval-blue-600: #69708e;
  --color-mediaeval-blue-700: #545972;
  --color-mediaeval-blue-800: #3c4254;
  --color-mediaeval-blue-900: #292d3b;
  --color-mediaeval-blue-950: #171a25;
}

SCSS

$mediaeval-blue: #2e3450;
$mediaeval-blue-rgb: 46, 52, 80;
$mediaeval-blue-light: mix(#fff, $mediaeval-blue, 20%);
$mediaeval-blue-dark: mix(#000, $mediaeval-blue, 20%);

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