[SimeVidas]

But why are the aspect ratios based on popular smartphone screens? Notice how on the website, you select a smartphone model, and then the button on the right shows CSS code for creating an aspect ratio that matches that smartphone’s screen. What’s the use case of having an element whose aspect ratio mimics that of popular smartphone screens?

[ryanhefner]

If you happen to have a product video in your site that has been formatted for a specific phone, you can make sure the container of the video is set as the same aspect ratio of the phone.

I also see the CSS as an add-on, the devices for me are more for reference, but I have used the CSS here and there for some of the Apple phones.