Your media query css needs to be wrapped in brackets too
@media (max-width: 1199px) {
#region-main-settings-menu.has-blocks, #region-main.has-blocks {
width: 100%;
}
}Moodle doesn't have a 'backend' and 'frontend' as (for example) WordPress.
You are free to use a different theme for an individual user, such as the Administrator, or to construct a theme that looks different on certain pages, such as Settings.
However, other than the Site Admin role, roles in Moodle are applied at a context level, not at a site level - ie a user could be a teacher in one course, but a student in another, and even within that system, permissions can be tweaked so that an individual user (or role) can access settings and other 'backend' pages which the core default permissions may not normally give them. So constant switching between different interfaces would be disconcerting for many (IMO). Moodle is far more than a CMS, with far more complex activities, settings, roles and permissions, so has a different way of working to simpler systems.
'Incredibly bizarre' No, just what you are used to - I find it (although getting used to) weird that in WP I have to go to a totally different interface to edit anything, where in Moodle (which is what I got used to at first), I can edit in place provided permissions allow. To me, that is the natural behaviour and what I would want to see in a system - but I don't go around calling WordPress 'bizarre' because it doesn't work the same way as Moodle.