I see ticking that option forces the main content to span fully but, I was looking to create sections which span the full width of that main content area as opposed to adjusting it’s width – the same way the Sections add-on allows.
So if I create one Section and set it’s background to black for example, that background applies across 100% of the width of the main content area (including when it’s ‘contained’). But if I do the same for the ‘test’ div in that snippet above, the background only applies to that cell.
I don’t know whether I maybe need to create a div before grid-container (to act as a section)? With other grids I’ve used doing something like that would break the grid.