#427D8B

CSS

:root {
  --mysterious-blue: #427d8b;
  --mysterious-blue-rgb: 66 125 139;
  --mysterious-blue-oklch: oklch(0.555 0.065 215);
}

.element {
  color: var(--mysterious-blue);
  background-color: hsl(192 36% 40%);
  border-color: oklch(0.555 0.065 215);
}

Tailwind CSS v4

@theme {
  --color-mysterious-blue: #427d8b;
  --color-mysterious-blue-50: #e1faff;
  --color-mysterious-blue-100: #d1eef6;
  --color-mysterious-blue-200: #b6dce7;
  --color-mysterious-blue-300: #92c0cd;
  --color-mysterious-blue-400: #71a9b7;
  --color-mysterious-blue-500: #4f91a1;
  --color-mysterious-blue-600: #447b88;
  --color-mysterious-blue-700: #36626d;
  --color-mysterious-blue-800: #254850;
  --color-mysterious-blue-900: #193238;
  --color-mysterious-blue-950: #091e22;
}

SCSS

$mysterious-blue: #427d8b;
$mysterious-blue-rgb: 66, 125, 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);
}