Check out example codes for "add shadow to UIButton swift". It will help you in understanding the concepts better.

Code Example 1

globeButton.setImage(UIImage(named: "Globe"), forState: .Normal)
globeButton.backgroundColor = UIColor(red: 171/255, green: 178/255, blue: 186/255, alpha: 1.0)
// Shadow and Radius
globeButton.layer.shadowColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.25).CGColor
globeButton.layer.shadowOffset = CGSize(width: 0.0, height: 2.0)
globeButton.layer.shadowOpacity = 1.0
globeButton.layer.shadowRadius = 0.0
globeButton.layer.masksToBounds = false
globeButton.layer.cornerRadius = 4.0

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