How to edit mobile version in bigcommerce.com builder?

Question

css

Hello.
There is an online store website template on the bigcommerce.com constructor . The problem is that I can’t find any information on how and where to edit the mobile template of this online store. Everything is ok in the browser, but when you open it on your phone, the viewport does not seem to work, and the mobile version of the site is not enabled. And when it is enabled, a standard template is displayed, and I can’t find it anywhere where it is located.
Who came across such a constructor, please tell me how to properly edit the template for your design. And how to set up a mobile version of the site.
Thank you.