func buttonConstraint() {
  // Center button in Page View
  NSLayoutConstraint(
    item: button,
    attribute: .CenterX,
    relatedBy: .Equal,
    toItem: view,
    attribute: .CenterX,
    multiplier: 1.0,
    constant: 0.0)
    .active = true
  
  // Set Width to be 30% of the Page View Width
  NSLayoutConstraint(
    item: button,
    attribute: .Width,
    relatedBy: .Equal,
    toItem: view,
    attribute: .Width,
    multiplier: 0.3,
    constant: 0.0)
    .active = true
  
  // Set Y Position Relative to Bottom of Page View
  NSLayoutConstraint(
    item: button,
    attribute: .Bottom,
    relatedBy: .Equal,
    toItem: view,
    attribute: .Bottom,
    multiplier: 0.9,
    constant: 0.0)
    .active = true
}