#42A5D2

CSS

:root {
  --mystic-blue: #42a5d2;
  --mystic-blue-rgb: 66 165 210;
  --mystic-blue-oklch: oklch(0.683 0.112 231.5);
}

.element {
  color: var(--mystic-blue);
  background-color: hsl(199 62% 54%);
  border-color: oklch(0.683 0.112 231.5);
}

Tailwind CSS v4

@theme {
  --color-mystic-blue: #42a5d2;
  --color-mystic-blue-50: #d7fbff;
  --color-mystic-blue-100: #c4efff;
  --color-mystic-blue-200: #a5ddfd;
  --color-mystic-blue-300: #7bc1e8;
  --color-mystic-blue-400: #4faad5;
  --color-mystic-blue-500: #0c92c3;
  --color-mystic-blue-600: #137ca4;
  --color-mystic-blue-700: #106384;
  --color-mystic-blue-800: #054961;
  --color-mystic-blue-900: #043344;
  --color-mystic-blue-950: #001e2c;
}

SCSS

$mystic-blue: #42a5d2;
$mystic-blue-rgb: 66, 165, 210;
$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);
}