Building a new UI surface

The app has one visual voice — "Matchday", a broadcast-graphics look. New surfaces should be indistinguishable from existing ones. Reuse first, then compose, then style.

1. Reuse before you build

Read src/components/ui/index.ts before writing markup. It already exports:

Card / CardHeader / CardBody · Button · Badge · ProgressBar · Select · Checkbox · DatePicker · CountryFlag · TeamLocation · PlayerAvatar · TeamLogo · InjuryBadge · JerseyIcon · ThemeToggle · PitchToken · AssetImage · GeneratedAvatar · GeneratedCrest · CountryCombobox

Also check before writing a helper:

• src/lib/ — formatting and domain helpers (finance.ts, playerSquad.ts, playerRoles.ts, countries.ts, dateFormatting.ts, seasonContext.ts, playerOvr.ts, …)
• src/hooks/ — useAdvanceTime, useFetchedSquad, useUndoRedo, useAssetDataUrl, …
• src/services/ — every backend call. Components never call invoke() directly.

A new component belongs in src/components/ui/ only if a second feature will use it. Otherwise put it in the feature folder (src/components/squad/, src/components/transfers/, …).

2. Design tokens

Colours and fonts come from the @theme block in src/App.css. Nothing else defines them.

• Never a hex literal or an arbitrary value (bg-[#10b981]) in a component.
• Every colour class needs its dark: partner. Light and dark both ship.
• Light surfaces are white / gray-100; their dark counterparts are navy-800 / navy-900.

src/components/ui/Button.tsx is the reference for how variants, sizes, and states are composed — read it before inventing a new pattern.

3. Accessibility floor

Not optional, and cheap if done while writing rather than after.

• Focus is visible. Every interactive element: focus:outline-none focus:ring-2 focus:ring-offset-2 focus:ring-<token> plus dark:focus:ring-offset-navy-800. Removing an outline without replacing it is a bug.
• Semantic elements. <button> for actions, <a> for navigation, <table> for tabular data, headings in order. A div with onClick is not keyboard reachable.
• Icon-only controls get an accessible name — aria-label={t("…")}, a translated string.
• Modals trap focus, close on Escape, restore focus to the trigger, and are labelled (role="dialog" + aria-labelledby).
• Lists and tables that sort or filter announce their state (aria-sort, aria-live for result counts).
• Colour is never the only signal. Pair it with a label, icon, or shape — this matters for the form/condition/morale indicators especially.
• Contrast holds in both themes. Gold on white and mid-emerald on navy are the usual failures.
• Respect prefers-reduced-motion for anything that animates on its own.

4. Strings

Every visible string — and every aria-label, title, placeholder, and alt — is a translation key in all 11 locales. Use /add-ui-string; don't hand-roll it.

5. State

• Zustand stores in src/store/. Never mutate store state from a component — copy, then set. (fix/hometab-store-mutation is the regression that made this a rule.)
• Backend data flows through src/services/*Service.ts.
• Derive, don't duplicate. If a value can be computed from the store, compute it.

6. Test it

Co-locate Foo.test.tsx next to Foo.tsx. Write it first.

// Query by role and accessible name. If this line fails, the component
// is not accessible — the test is doing double duty.
const save = screen.getByRole("button", { name: /save/i });

• Query by role/label, never by class or test id.
• Pure logic goes in a *.helpers.ts file and gets unit-tested directly — src/components/squad/SquadTab.helpers.ts is the pattern.
• Cover the keyboard path, not just the click path, for anything interactive.

npx vitest run src/components/<area>
npx tsc --noEmit

7. Invariants, if you touch squad, tactics, or the pitch

• XI slot alignment — starting-XI array entry i is formation slot i. Substitutions insert at the vacated index; never append or re-sort. Slot geometry comes from buildPitchRows(formation) in src/components/squad/SquadTab.helpers.ts, and PitchToken is the shared token component.
• Deployed vs natural position — player.position is the natural position and is never mutated. Where a player is currently deployed comes from getDeployedPosition(team, slot). Role pickers and validators use the deployed slot; player descriptions use the natural position.

Checklist

• Searched src/components/ui/index.ts, src/lib/, src/hooks/ before writing anything new
• Token classes only — no hex literals, no arbitrary values
• Every colour class has a dark: partner; checked in both themes
• Visible focus ring on every interactive element
• Semantic elements; icon-only controls have translated aria-labels
• All strings routed through /add-ui-string (all 11 locales)
• No store mutation from a component
• Co-located test querying by role, written before the component
• npx vitest run src/components/<area> and npx tsc --noEmit green