#383B56

CSS

:root {
  --mediaeval-blue: #383b56;
  --mediaeval-blue-rgb: 56 59 86;
  --mediaeval-blue-oklch: oklch(0.362 0.047 278.9);
}

.element {
  color: var(--mediaeval-blue);
  background-color: hsl(234 21% 28%);
  border-color: oklch(0.362 0.047 278.9);
}

Tailwind CSS v4

@theme {
  --color-mediaeval-blue: #383b56;
  --color-mediaeval-blue-50: #f2f4ff;
  --color-mediaeval-blue-100: #e5e6f8;
  --color-mediaeval-blue-200: #d0d2e8;
  --color-mediaeval-blue-300: #b2b5d0;
  --color-mediaeval-blue-400: #989cba;
  --color-mediaeval-blue-500: #7f83a5;
  --color-mediaeval-blue-600: #6b6f8c;
  --color-mediaeval-blue-700: #565970;
  --color-mediaeval-blue-800: #3e4153;
  --color-mediaeval-blue-900: #2b2d3a;
  --color-mediaeval-blue-950: #181a24;
}

SCSS

$mediaeval-blue: #383b56;
$mediaeval-blue-rgb: 56, 59, 86;
$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);
}