A simple view with border and rounded corners that renders on storyboard

RoundedView.swift

import UIKit

@IBDesignable class RoundedView: UIView {

    @IBInspectable var cornerRadius: CGFloat {
        get {
            return layer.cornerRadius
        }
        set(newRadius) {
            layer.cornerRadius = newRadius ?? 0
            layer.masksToBounds = newRadius > 0
        }
    }
    
    @IBInspectable var borderWidth: CGFloat {
        get {
            return layer.borderWidth
        }
        set(newWidth) {
            layer.borderWidth = newWidth
        }
    }
    
    @IBInspectable var borderColor: UIColor? {
        get {
            if let layerColor = layer.borderColor {
                return UIColor(CGColor: layerColor)
            }
            return nil
        }
        set(newColor) {
            layer.borderColor = newColor?.CGColor
        }
    }
    
    required init(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)!
    }
    
    override init(frame: CGRect) {
        super.init(frame: frame)
    }
}