Put a group on the page that is the same width as the side menu and label it ‘side buffer’…the side menu should be a floating group so as to ‘cover’ the ‘side buffer’…If you page is 1200px for example, and the side buffer and side menu are 280px then you have another 920px of space…what you do is to have a group that you label ‘container’ to have all your content.
Make sure responsive settings have the ‘container’ set to collapse width and set it to something high like 4200px.
Then when the side menu is supposed to be hidden, you should also hide the ‘side buffer’…this should do the trick…
Another way is to have a group called ‘container’ that you put a left margin set to 280px using conditionals when the side menu is visible, and make the left margin 0 px when the side menu is not visible.
Either method works, but I forget if there is a bit of difference between how they function…If I remember correct the latter will ‘push’ the content off screen while the former will just readjust the content to fit if your responsive settings are done properly.