Layout: Sidebar
The sidebar layout creates a container, inside of which a larger panel can sit next to a smaller (sidebar) panel.
The two panels stack vertically, until there is enough horizontal space for them to sit alongside each other. The point at which this change happens is determined by setting a flex-basis
on the sidebar panel and a min-width
on the larger panel. No viewport media queries required, so it will nest nicely inside of other containers.