I am wanting to hide the sidebar in gantry 5 using the hydrogen template. In the past with ganry 4 this has happened automatically so I haven't had to consider how it is done. I assume this would be done in the new custom.scss file using an @media query, but I am not sure how to get started on this. Considering my expected users I don't think it would be a good idea to use rem yet.
If this is a site that is online (just installed, dev or live) could you please supply a link in the Public or SECURE part of your reply so we can better diagnose the issue?
It makes our suggestions more accurate if we see the actual coding of your site.