 
     override public var intrinsicContentSize: CGSize {
         return contentView.intrinsicContentSize
+    }
+
+    public override func layoutSubviews() {
+        cardNumberFieldBackground.roundingCorners(corners: .allCorners, radius: 4.0)
+        expirationFieldBackground.roundingCorners(corners: .allCorners, radius: 4.0)
+        cvcFieldBackground.roundingCorners(corners: .allCorners, radius: 4.0)
+        cardHolderFieldBackground.roundingCorners(corners: .allCorners, radius: 4.0)
     }
 
     // MARK: CardFormView


    /// 各Viewのセットアップ
    private func setupViews() {
        cardNumberFieldBackground = UIView()
        expirationFieldBackground = UIView()
        cvcFieldBackground = UIView()
        cardHolderFieldBackground = UIView()

        cardNumberErrorLabel = UILabel()
        expirationErrorLabel = UILabel()

        inputStackView.translatesAutoresizingMaskIntoConstraints = false
        inputStackView.addArrangedSubview(textField)

        backgroundView.backgroundColor = FormStyle.defaultStyle.inputFieldBackgroundColor
        backgroundView.addSubview(inputStackView)

