#42A5CE

CSS

:root {
  --mystic-blue: #42a5ce;
  --mystic-blue-rgb: 66 165 206;
  --mystic-blue-oklch: oklch(0.681 0.109 229);
}

.element {
  color: var(--mystic-blue);
  background-color: hsl(198 59% 53%);
  border-color: oklch(0.681 0.109 229);
}

Tailwind CSS v4

@theme {
  --color-mystic-blue: #42a5ce;
  --color-mystic-blue-50: #d7fcff;
  --color-mystic-blue-100: #c4efff;
  --color-mystic-blue-200: #a5ddfb;
  --color-mystic-blue-300: #7bc2e5;
  --color-mystic-blue-400: #4fabd2;
  --color-mystic-blue-500: #0e93bf;
  --color-mystic-blue-600: #147ca1;
  --color-mystic-blue-700: #116382;
  --color-mystic-blue-800: #06495f;
  --color-mystic-blue-900: #053343;
  --color-mystic-blue-950: #001e2b;
}

SCSS

$mystic-blue: #42a5ce;
$mystic-blue-rgb: 66, 165, 206;
$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);
}