#3FA5D1

CSS

:root {
  --mystic-blue: #3fa5d1;
  --mystic-blue-rgb: 63 165 209;
  --mystic-blue-oklch: oklch(0.681 0.113 230.3);
}

.element {
  color: var(--mystic-blue);
  background-color: hsl(198 61% 53%);
  border-color: oklch(0.681 0.113 230.3);
}

Tailwind CSS v4

@theme {
  --color-mystic-blue: #3fa5d1;
  --color-mystic-blue-50: #d6fcff;
  --color-mystic-blue-100: #c3efff;
  --color-mystic-blue-200: #a4ddfd;
  --color-mystic-blue-300: #7ac2e8;
  --color-mystic-blue-400: #4daad4;
  --color-mystic-blue-500: #0093c2;
  --color-mystic-blue-600: #0d7ca4;
  --color-mystic-blue-700: #0c6384;
  --color-mystic-blue-800: #024961;
  --color-mystic-blue-900: #033344;
  --color-mystic-blue-950: #001e2c;
}

SCSS

$mystic-blue: #3fa5d1;
$mystic-blue-rgb: 63, 165, 209;
$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);
}