WIP: Enable grid visual overlays during development
This is just a convenience feature for development; it does not affect the live site.
The visual overlay shows the grid used for pages following the new design.
Enabling this helpful feature required editing
Instead, the overlay should be always be enabled during development.
An overlay is displayed when the width of a page is 390px (the smallest
or 750px (the smallest
No overlay is displayed at other widths.