Confirm that:
- default selection is extra-wide
- the 4 options are present (narrow, wide, extra-wide, and full width)
- appropriate classes get added to the section tag
Styling is dependent on the other merge request.
With styling present:
- narrow should be 496px wide
- wide should be 753px wide
- extra-wide should be the width of the footer
- full width should be 100% of the page width (the last two were already present, but we should confirm they are unchanged.)