#427F8B

CSS

:root {
  --mysterious-blue: #427f8b;
  --mysterious-blue-rgb: 66 127 139;
  --mysterious-blue-oklch: oklch(0.56 0.066 211.9);
}

.element {
  color: var(--mysterious-blue);
  background-color: hsl(190 36% 40%);
  border-color: oklch(0.56 0.066 211.9);
}

Tailwind CSS v4

@theme {
  --color-mysterious-blue: #427f8b;
  --color-mysterious-blue-50: #e1fbff;
  --color-mysterious-blue-100: #d0eef5;
  --color-mysterious-blue-200: #b5dce5;
  --color-mysterious-blue-300: #91c1cc;
  --color-mysterious-blue-400: #70a9b5;
  --color-mysterious-blue-500: #4d929f;
  --color-mysterious-blue-600: #427b87;
  --color-mysterious-blue-700: #35636c;
  --color-mysterious-blue-800: #25494f;
  --color-mysterious-blue-900: #183237;
  --color-mysterious-blue-950: #091e22;
}

SCSS

$mysterious-blue: #427f8b;
$mysterious-blue-rgb: 66, 127, 139;
$mysterious-blue-light: mix(#fff, $mysterious-blue, 20%);
$mysterious-blue-dark: mix(#000, $mysterious-blue, 20%);

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