Why we will not let you write custom CSS on your product page

The ask, and the answer

Most brands ask for a stylesheet within a week of seeing their first consumer product page, and the answer is no. Here is why, since a policy line on its own would be irritating.

Product pages are themed with a fixed set of typed tokens: colours, a type scale and a space scale. There is no <style> you can reach and no class you can target.

Why a stylesheet is different from a token

A token has a type and a range. A stylesheet has neither.

The type scale and the space scale carry enforced floors, so a token set cannot shrink text below a legible size or collapse the space around a block, however it is filled in. A stylesheet can do both, in one line, by accident, on a page nobody re-reads before it goes live.

The block this protects is the allergen and safety information, which on some products is the reason the page exists at all. A theme that can make it small, faint or crowded is a theme that can make it invisible while the page still looks fine to whoever approved it.

What you can still change

More than most people expect: the palette, the type scale within its floors, the space scale within its floors, your logo and your product photography. It is a real theme, and two brands’ pages do not look alike.

What you cannot do is reach past it, and you are finding that out here rather than three weeks into a build.

The other half of the reason

Consumer pages make zero third-party requests. No analytics, no font CDN, no embedded media — third-party media renders as a link-out card instead. A custom stylesheet is an arbitrary URL away from breaking that, and it is enforced by a content security policy rather than by asking nicely.

A page that answers a scan is infrastructure. Infrastructure with an extension point is a page that can be broken by someone who was only trying to move a heading.