I have a layout page that I am using Layouts to edit with.
I have 4 rows that all use the 'Row as wide as post content' row type but I want to wrap all four of these rows in another div that has a background colour that stretches the full width of the screen i.e. 'Row as wide as Bootstrap container - full width of screen'
Hi, "full width of screen" isn't usually achievable unless your theme is integrated with Layouts. Normally Layouts takes over the main content area of the theme, and can extend only to the edges of that content area. Normally the theme controls the header and footer area, as well as the sidebar. You can see in the row settings that the background doesn't extend full screen width, only the width of the container, and the right column sidebar (gray area controlled by the theme) isn't affected. I'm attaching a screenshot here for your reference.
To achieve something like you see here in the screenshot, you can use a Grid cell in your layout that contains 4 rows and any number of columns. Use the row settings to apply the "Row as wide as Bootstrap container its background extends to full width" setting.