This test adapts to the device that you run it on. Ideally, therefore, you need to access it from an appropriate device (iPhone, iPad, Android phone or tablet) to get 100% fidelity of rendering.
You can run it from a desktop browser but if you do you will need to take some steps to make it work properly at all, and when you do you may find that there are slight rendering differences (because, for example, Windows machines do not normally have the Helvetica Neue font available).
One way to run it on a desktop browser is: