Marketing and Product Are Two Surfaces of One Brand

The public site sells; the product is used. A visitor reads one marketing page for ninety seconds and leaves. An operator opens the same brand every morning and stays for hours. Designing both to one specification produces either a brochure that is exhausting to work in or a product screen that cannot sell anything.

So the two surfaces should diverge. The question is never whether, it is which layer is allowed to diverge.

Marketing and product are the pair that forces the question, because they are the two nobody can pretend are the same job. But the rule underneath is not about two. Most brands run four or five surfaces: the site, the product, the documentation, the transactional email, the status page, sometimes a sales deck. Each one is a different job for a different reader at a different moment. The brand owns the layer; every surface chooses from it. Adding a sixth surface then changes nothing about the rule, which is the test of whether the rule was right.

Where a new surface belongs is settled by the same question the layer rule asks, not by which team built it. Docs are read for minutes at a time by someone mid-task, so they sit near the product on density and near the site on reading width. Transactional email has no theme control and no hover, so it takes the shared values and little else. Neither is a special case; both are the general rule applied.

The Layer Rule

Brand values are shared. Application values are chosen per surface.

If a value answers who are we, it is shared. If it answers what is this screen for, it is the surface's own call. A product screen picking a tighter radius is design. A product screen picking a different blue is drift.

What Legitimately Differs

These divergences are healthy and worth stating explicitly rather than letting them happen by accident:

• Type scale. Marketing lives in the display registers and has real hero sizes. Product lives two or three steps down, with the small end of the scale carrying most of the interface. The scale is the same ladder; the two surfaces stand on different rungs.
• Weight. Marketing leans bold, because a headline is competing for attention. Product leans medium and semibold, because everything on screen is already wanted.
• Radius. Marketing can afford larger, softer cards: few elements, lots of air. Product goes tighter, because at high density large radii eat the corners of adjacent elements and read as mushy. Between them the two surfaces may well use five or six steps, and that is not a broken scale as long as every step is drawn from the same ladder. What breaks it is a value that is on no ladder at all.
• Density and width. Marketing measures a reading column, because the limit is what an eye tracks across a line of prose. Product measures a work area, because the limit is the data, and the data does not get narrower on a wider screen. That is also why the width belongs to the shell rather than the page: a product where each page picks its own column is a product where the content jumps sideways on every navigation.
• Motion. Marketing may animate on entry, because nothing has been asked of the visitor yet. Product animates in response to the user, with two standing exceptions: onboarding, where motion is what shows a first-time user where a thing came from, and empty states, where it says the screen is waiting rather than broken. Both are answers to a user's situation, which is why they do not contradict the rule.
• Theme. A product may need light mode when the marketing site does not. Someone using a tool for six hours has a right to choose; a visitor passing through does not need the switch.

Components That Render on Both

The header, the primary call to action, the pricing widget, the footer: a handful of components appear on both surfaces, and they are where a surface rule turns into an argument. They belong to neither surface.

The rule: a shared component reads its surface from context, it does not carry a variant per surface. A component with a marketing prop and an app prop has already forked; the two branches drift on the next change and nobody notices, because both still render.

What that means in practice:

• The component takes tokens from the surface it is mounted in. If the product is themed and the site is not, the component is theme-aware everywhere and the site simply never changes the value.
• Surface-specific size is a prop the component already has. A call to action large on a landing page and medium in a toolbar is one component at two sizes, not two components.
• If the two surfaces genuinely need different behaviour rather than different sizing, that is two components with two names. Say so out loud instead of hiding the fork behind a boolean.
• A shared component's owner is the token source's owner, not whichever team touched it last.

What Is Drift, Not Divergence

• A second grey, or a second brand blue, that exists only on one surface
• A component that means one thing in the site and another in the product: a pill that is a link here and a label there
• Contrast that meets the floor on the marketing page and quietly drops below it in the dense product screen, where small text makes it worse
• Interaction affordances present on one surface only: focus-visible states, keyboard paths and ARIA roles that the product has and the site lacks, or the reverse

The Token Layer Must Be Single

This is where one codebase serving both surfaces usually fails, and it fails invisibly.

The failure looks like three mechanisms carrying the same values at once: CSS custom properties defined once, literal hex values pasted into markup, and a runtime helper that returns class names per theme. Each arrives for a good local reason. Together they mean a colour cannot be changed in one place, and nothing reports the mismatch.

The rule: one source of truth for values, any number of consumers. A themed surface resolving tokens at runtime is fine as long as it resolves the shared tokens rather than holding its own copies. The test is mechanical: change the brand accent in one place and see whether both surfaces move. If one does not, you have two design systems wearing one logo.

Literal values in markup are the specific thing to hunt, for two checkable reasons: a token audit does not see them, and a theme cannot reach them. A surface full of literals has not opted out of theming, it has quietly made theming impossible.

Where the Boundary Actually Sits

More often than a stray hex, the second blue arrives at a repository or system boundary. Where the boundary falls decides what work the single source needs:

• One repository, both surfaces. Easiest case, and the one most likely to fail anyway. The values must live outside both surfaces' folders, or the surface built first quietly becomes the definition.
• Separate repositories. The source has to be a published, versioned artifact that both consume, and updating it has to be a release rather than a copy. If the honest answer to "how does the site get the new accent" is "someone pastes it", there is no single source, only a habit.
• A CMS or marketing platform beside the product. The values have to be exported into the platform's own theming as a build step, not re-entered by hand in an admin screen. Anything typed into a settings field is a fork with no history.
• A design tool as the origin. Fine, as long as one direction is authoritative. Two-way sync between a design tool and code is not a single source, it is two sources with a merge conflict on a delay.

The cost of crossing a boundary is what people actually optimise for. If consuming the shared source is slower than hardcoding the value, the value gets hardcoded, and no rule survives that.

Someone Owns the Source

A source of truth owned by everyone is owned by nobody, and this is the failure that outlives every other point here. The tokens go stale, each surface patches locally because asking is slower, and the split is complete before anyone proposes it.

Name one owner for the token source: a person or a single team, written down where the tokens live. The owner does not decide what each surface looks like. They decide what goes into the shared layer, they review changes to it, and they are the person a surface team asks before adding a value.

Two further rules make the ownership real rather than nominal:

• Adding to the shared layer is the owner's call. Choosing from it is not. If the owner is consulted on every radius a page uses, they become a bottleneck and get routed around within a month.
• The owner is accountable for the boundary being cheap to cross. If teams keep hardcoding values, that is the owner's problem to fix, not the teams' discipline to blame.

Getting There From a Fork

Most readers arrive here already forked, and a rule about the correct end state is not a plan. The order matters, because doing it in the obvious order fails.

1. Inventory before you unify. List every value each surface actually uses, from the running surfaces rather than from the documentation. The gap between the two is the real subject.
2. Separate collision from duplication. Two surfaces holding the same value in two places is duplication, and it is cheap to fix. Two surfaces holding different values for one role is a collision, and it needs a decision by a person. Do not let a tool pick the winner by frequency.
3. Settle the collisions first, on paper. One accent, one grey per role, one radius ladder. This is a design decision, not a refactor, and it is the only step that cannot be automated.
4. Then make the source and point one surface at it. One, not both. A source proven against a single consumer is a source; a source written for two consumers at once is a guess about both.
5. Move the second surface, and delete the old values in the same change. A migration that leaves the old mechanism in place has added a mechanism rather than removed one, which is how three arose in the first place.
6. Add the check that fails the build. Until a literal value in markup can break CI, the count only goes up, and the fork rebuilds itself at whatever rate the team ships.

The step teams skip is the third, because it is the one requiring someone to overrule a surface they do not own. That is exactly what the owner is for.

Practical Checks

• Extract both surfaces and diff the palettes. Any hue present on one and absent on the other is a question to answer, not a fact to accept.
• List the radius values in use across both surfaces. Not the count: the question is whether every value is a step of the declared scale. One off-ladder value matters more than six on-ladder ones.
• Check contrast on the smallest text of the product's densest screen, not on marketing body copy: 4.5:1 for body text, 3:1 from 18.66px bold or 24px regular up. The marketing page passes on size alone and tells you nothing about the screen that will fail.
• Grep for literal colour values in markup. The count is the drift debt, and it only goes up on its own.

See also: ui-density for choosing the product's density, color-mode-and-theme for adding a theme to one surface, component-family-consistency for keeping a component meaning one thing everywhere.