# Fluid Typography

## Objective

Let type grow smoothly with the viewport instead of jumping at every breakpoint.

Viewport-interpolated sizing for the existing type steps, bounded by a defined floor and ceiling.

## Before You Begin

This feature is being added to an application that already exists and already
works. Do not scaffold a new project, and do not assume a blank slate.

Inspect the codebase first and establish:

- The existing application structure and where code of this kind already lives.
- The framework and version in use.
- The existing design system — colours, spacing, typography, and component conventions.
- Existing UI components you can reuse instead of writing new ones.
- The existing database structure, if this feature needs to persist anything.
- The existing authentication and authorization system, if this feature is user-scoped.
- Dependencies already installed, so you don't add a library that duplicates one.
- The existing test setup and conventions.

Only start writing code once you understand the above. If the application
already implements part of this feature, extend it rather than replacing it.

## Implementation Instructions

1. Apply interpolation to the steps already defined by Typography Scale rather than inventing new sizes. That feature owns which steps exist; this one owns how each one behaves between the narrowest and widest viewport.
2. Give every fluid step an explicit minimum and maximum. An unbounded rule produces unreadable type on a small phone and absurd type on an ultrawide monitor, and both ends will be found by real users.
3. Scale the display and heading steps more aggressively than body copy. Body text has a comfortable size that does not change with the window, and growing it with the viewport makes wide screens harder to read, not easier.
4. Adjust line height as the size changes — large type wants proportionally tighter leading than small type — otherwise headings that looked correct on a phone become airy and loose on a desktop.
5. Do not express the interpolation purely in viewport units. A size that ignores the root font size stops responding to browser zoom and to the user's own text-size preference, which is a straightforward accessibility failure.

## UI and UX Requirements

Match the application's existing design system exactly. Reuse its components,
spacing, and typography. This feature should look like it was always there.

## Responsive Requirements

Works on mobile, tablet, and desktop. Touch targets are large enough to hit on a
phone, and nothing overflows horizontally at 320px.

## Accessibility Requirements

- Fully keyboard navigable.
- Correct semantic elements and ARIA roles.
- Visible focus states.
- Meets WCAG AA contrast.
- Dynamic changes are announced to screen readers.
- Respects prefers-reduced-motion.

## Edge Cases

- Every fluid step needs a clamped floor and ceiling, since the interpolation is a straight line and will happily continue past the point of legibility in both directions.
- Sizes derived from viewport units alone do not respond to browser zoom, so the setting a low-vision user relies on stops working exactly where they need it.
- Line height must be interpolated alongside size, or the leading that suited the smallest step leaves large headings looking disconnected from themselves.
- Large display steps set for a desktop hero will overwhelm a narrow screen and wrap into four lines, so the floor for those steps needs to be much lower than their proportional value suggests.
- Interpolation driven by the viewport misbehaves inside constrained columns, sidebars, and dialogs, where the available width has nothing to do with the window width.
- Text that resizes continuously during a window drag or a device rotation causes reflow of everything below it; verify that nothing measured in a fixed pixel height sits beside fluid text.
- Values that land on fractional pixels can render inconsistently across browsers, so check the interpolated sizes at real viewport widths rather than only at the two endpoints.

## Testing

Exercise the feature end to end in the running application. Cover every edge case
above, then run the existing test suite and confirm nothing regressed.

## Acceptance Criteria

- [ ] Type sizes change continuously across viewport widths with no jump at a breakpoint.
- [ ] Every fluid step has an enforced minimum and maximum size.
- [ ] Type still responds correctly to browser zoom and user text-size settings.
- [ ] Line height is interpolated together with size at every step.
- [ ] Body copy scales conservatively while display steps scale more.
- [ ] Headings do not overflow or wrap awkwardly at the narrowest supported width.
- [ ] The step definitions themselves remain owned by Typography Scale.
- [ ] The feature matches the existing design system.
- [ ] No existing functionality is broken.

## Adaptation Rules

- Match the existing design system. Do not introduce a new colour palette,
  spacing scale, or component library.
- Reuse existing components and utilities wherever they fit.
- Follow the naming, file layout, and code style already present.
- Do not upgrade, replace, or remove existing dependencies to make this
  feature fit. Adapt the feature to the app, not the app to the feature.
- Do not break existing functionality. If a change is genuinely required in
  existing code, make the smallest one that works and say so.
- If something in these instructions conflicts with how the application is
  built, follow the application and explain the deviation.

## Final Verification

Before you report the work as done:

1. Re-read the acceptance criteria above and check each one against what you
   actually built.
2. Run the application and exercise the feature end to end.
3. Run the existing test suite and confirm you have broken nothing.
4. Check the feature on mobile, tablet, and desktop widths.
5. Check keyboard navigation and focus handling.
6. Summarize what changed: files added, files modified, and anything you
   deliberately did differently because of how this application is built.

If any acceptance criterion is unmet, fix it before reporting completion.