how can I emulate iMac Retina 5K through chrome dev tools and target through CSS?

I've been working on a clients website and they have recently bought an iMac retina 5k. Since they have bought this the text on the website has shrunk so that its hardly readable. My main question is how can I emulate this in Chrome dev tools. I understand that the screen dimensions are 5120px by 2880px. What is the dpr for these devices and how can I target them using CSS?