Sixteen pixels, or the checkout jumps
Most of the storefront pieces in this app are text and a pair of dropdowns. They inherit the shop’s own typography, so they adapt with the page rather than needing a layout of their own. Two things had to be deliberate.
box-sizing: border-box on the picker’s dropdowns. width: 100% plus
padding overflows its container otherwise, and on a narrow phone that pushes
the entire checkout sideways. The customer gets a horizontal scrollbar on a
payment page, which is exactly the moment to not look amateur.
A 16px font on those dropdowns, not 14. iOS Safari zooms the whole page when an input with a smaller font takes focus. The customer taps the collection time and the checkout lurches. Nothing is broken, but it reads as broken — and it reads as broken at the point of payment, which is the single worst place on the site to lose someone’s confidence.
It is the one place the type size is not inherited from the shop, and that is a deliberate exception rather than an oversight. A shop that sets 14px everywhere gets 16px here, because the alternative is a checkout that jumps.
Both of these are the sort of thing that never appears in a bug report. Nobody writes “the page zoomed slightly when I tapped the dropdown”. They abandon the basket, and the shop sees a conversion number with no explanation attached to it.