#5BA3C7

CSS

:root {
  --mystic-blue: #5ba3c7;
  --mystic-blue-rgb: 91 163 199;
  --mystic-blue-oklch: oklch(0.683 0.09 231.9);
}

.element {
  color: var(--mystic-blue);
  background-color: hsl(200 49% 57%);
  border-color: oklch(0.683 0.09 231.9);
}

Tailwind CSS v4

@theme {
  --color-mystic-blue: #5ba3c7;
  --color-mystic-blue-50: #ddfaff;
  --color-mystic-blue-100: #cceeff;
  --color-mystic-blue-200: #afdbf5;
  --color-mystic-blue-300: #89c0df;
  --color-mystic-blue-400: #64a8ca;
  --color-mystic-blue-500: #3e90b7;
  --color-mystic-blue-600: #367a9b;
  --color-mystic-blue-700: #2b627c;
  --color-mystic-blue-800: #1c485b;
  --color-mystic-blue-900: #123240;
  --color-mystic-blue-950: #041e29;
}

SCSS

$mystic-blue: #5ba3c7;
$mystic-blue-rgb: 91, 163, 199;
$mystic-blue-light: mix(#fff, $mystic-blue, 20%);
$mystic-blue-dark: mix(#000, $mystic-blue, 20%);

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