// Create alert controller as usual
let alert = OKAlertController(title: "Some title", message: "Some message")

// Fill with reqired actions
alert.addAction("Some option", style: .Default) { _ in
  // Process action
}

alert.addAction("Cancel", style: .Cancel, handler: nil) // Ignore cancel action handler

// Setup alert controller to conform design
alert.titleFont = ... /// <- Title text font
alert.titleColor = ... /// <- Title text color
... /// <- Any other customisation

alert.show(fromController: self, animated: true)

extension OKAlertController {
  // For instance your style called "Minimalistic", just create function to show this style of alert
  func showMinimalistic() {
    // Get root UIViewController, or you could use any other
    guard let rootController = UIApplication.sharedApplication().delegate?.window??.rootViewController else {
      return
    }

    // Setup style before show
    self.shadowColor = UIColor(white: 1, alpha: 0.79)
    self.backgroundColor = UIColor.whiteColor()
    ... /// <- Any other customisation

    // Finaly show alert controller
    show(fromController: rootController, animated: true)
  }
}


// Somewhere in the code
let alert = OKAlertController(title: "Some title", message: "Some message")
... /// <- Fill with actions
// Show "Minimalistic" style provided by bellow extension
alert.showMinimalistic()