Swift implementation to highlight Cocoa UI elements (http://stackoverflow.com/a/25984748/316803)

highlight.swift

    // Taken from:
    // https://gist.github.com/joelcox/28de2f0cb21ea47bd789

    NSColor.selectedMenuItemColor.set()
    NSBezierPath(rect: rect).fill()

    if rect.height > 1 {
        let currentControlTint = NSColor.currentControlTint
        let startingAlpha: CGFloat = currentControlTint == .blueControlTint ? 0.16 : 0.09

        let gradient = NSGradient(starting: NSColor(white: 1, alpha: startingAlpha),
                                  ending: NSColor(white: 1, alpha: 0))
        let start = CGPoint(x: rect.minX, y: rect.maxY - 1)
        let end = CGPoint(x: rect.minX, y: rect.minY + 1)
        gradient?.draw(from: start, to: end, options: .drawsBeforeStartingLocation)

        if currentControlTint == .blueControlTint {
            NSColor(white: 1, alpha: 0.1).set()

            let smallerRect = CGRect(x: rect.minX, y: rect.maxY - 1, width: rect.width, height: 1)
            NSBezierPath(rect: smallerRect).fill()
        }
    }