Secondary Sidebar Widget disappears in mobile view

This Primer Theme has 3 column capability. When using the 3 column layout, this is how it shows:

Primary Sidebar | Main Page Content | Secondary Sidebar

When in tablet or smartphone (mobile) view this is what occurs.

Main Page Content
---
Primary Sidebar

The Secondary Sidebar disappears.

Cause of the disappearing Secondary Sidebar
This appears to be an intended design, because the main CSS for the theme shows the following:

#tertiary  {
display:none;
}	
}

Using Custom CSS, brings back the Secondary Sidebar in mobile view:

@media screen and (max-width: 976px) {
#tertiary  {
display: block;
}	
}

Suggestion
A sidebar full of content that is important to the website owner, is not a good idea to make it disappear like that. This only frustrates users because the majority of WordPress users are not skilled in CSS, let alone HTML. They just want to get a theme and use it to display their content.

In saying that, here is a suggestion, because making a sidebar disappear in mobile view is actually a good feature, but make it optional.

In fact, make it optional for both sidebars. You can add this option to the “Layout” panel where we choose the page/sidebar layout.

This works very much like widget option plugins where they provide visibility settings to choose which page the widget appears or disappears.

When adding this option as suggested, it replaces the need for widget option plugins for visibility purposes.

Thanks