fix(pages): missing margin/padding on page edges at certain breakpoints

[MaggieAppleton]

Problem

On the garden page, at certain viewport breakpoints there is no margin or padding on the left/right edges of the page. Content runs flush to the screen edge, which looks broken and is hard to read.

Steps to Reproduce

1. Navigate to the garden page
2. Resize the browser window through various breakpoints
3. At certain widths, the horizontal margin/padding disappears

Expected Behaviour

Consistent, appropriate margin/padding on both edges of the garden page at all breakpoints.