Editing mobile theme

There appears to be a different template file for the mobile theme, because the changes I’m making to the CSS file aren’t changing my site’s appearance on mobile. But when I’m on the site on mobile and click “view full site”, it shows me the site as I’d expect to see it, with the CSS changed applied.

So to get the mobile site to look how I want, I could either change the mobile template file’s CSS, or set mobile to only show the full site version, but I can’t figure out how to do either of these.

How can I edit mobile separately or only display the full site version?