UI UX Guidelines

UI/UX Implementation Details

Note: For high-level design rules (hit targets, focus rings, contrast, etc.), defer to vercel-design-guidelines which fetches live standards from Vercel. This skill provides implementation-specific details.

Interactions

Keyboard & Focus

• MUST: Full keyboard support per WAI-ARIA APG
• MUST: Manage focus (trap, move, return) per APG patterns
• MUST: Group focus with :focus-within where appropriate

Touch & Input

• MUST: touch-action: manipulation to prevent double-tap zoom
• MUST: Set -webkit-tap-highlight-color to match design
• MUST: Mobile <input> font-size ≥16px to prevent iOS zoom, or use:

  <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, viewport-fit=cover">
  

Form Behavior

• MUST: Hydration-safe inputs (no lost focus/value)
• NEVER: Block paste in <input>/<textarea>
• MUST: Enter submits text input; in <textarea>, Cmd/Ctrl+Enter submits
• MUST: Keep submit enabled until request starts; use idempotency key
• MUST: Allow submitting incomplete forms to surface validation
• MUST: Errors inline next to fields; on submit, focus first error
• MUST: autocomplete + meaningful name; correct type and inputmode
• SHOULD: Disable spellcheck for emails/codes/usernames
• SHOULD: Placeholders end with ellipsis and show example (e.g., sk-012345...)
• MUST: Warn on unsaved changes before navigation
• MUST: Compatible with password managers & 2FA
• MUST: Trim values to handle text expansion trailing spaces
• MUST: No dead zones on checkboxes/radios; label+control share hit target

State & Navigation

• MUST: URL reflects state (filters/tabs/pagination). Prefer nuqs
• MUST: Back/Forward restores scroll
• MUST: Links use <a>/<Link> (support Cmd/Ctrl/middle-click)

Feedback

• SHOULD: Optimistic UI with reconciliation; on failure show error or Undo
• MUST: Confirm destructive actions or provide Undo window
• MUST: Use polite aria-live for toasts/inline validation
• SHOULD: Ellipsis for follow-ups ("Rename...") and loading ("Saving...")

Touch/Drag

• MUST: Delay first tooltip; subsequent peers no delay
• MUST: overscroll-behavior: contain in modals/drawers
• MUST: During drag, disable text selection and set inert on dragged element

Animation

• SHOULD: Prefer CSS > Web Animations API > JS libraries
• MUST: Animations are interruptible and input-driven (avoid autoplay)
• MUST: Correct transform-origin (motion starts where it "physically" should)

Cross-Browser

• MUST: Apply CSS transforms to SVG children (<g>), not parent <svg>
• MUST: Set transform-box: fill-box and transform-origin: center on SVG
• SHOULD: Use translateZ(0) or will-change: transform for text anti-aliasing artifacts

Layout

• SHOULD: Optical alignment; adjust by +/-1px when perception beats geometry
• MUST: Deliberate alignment to grid/baseline/edges
• SHOULD: Balance icon/text lockups (stroke/weight/size/spacing/color)
• MUST: Verify mobile, laptop, ultra-wide (simulate at 50% zoom)
• MUST: Respect safe areas (env(safe-area-inset-*))
• MUST: Avoid unwanted scrollbars; fix overflows

Content & Accessibility

• SHOULD: Inline help first; tooltips last resort
• MUST: Skeletons mirror final content (avoid layout shift)
• MUST: <title> matches current context
• MUST: No dead ends; always offer next step/recovery
• MUST: Design empty/sparse/dense/error states
• SHOULD: Curly quotes (" "); avoid widows/orphans
• MUST: Tabular numbers for comparisons (font-variant-numeric: tabular-nums)
• MUST: Redundant status cues (not color-only); icons have text labels
• MUST: Use ellipsis character ... (not ...)
• MUST: scroll-margin-top on headings; include "Skip to content" link
• MUST: Resilient to user-generated content (short/avg/very long)
• MUST: Locale-aware dates/times/numbers/currency
• MUST: Use non-breaking spaces: 10 MB, Cmd + K
• MUST: Detect language via Accept-Language header, NOT IP geolocation

Performance

• SHOULD: Test iOS Low Power Mode and macOS Safari
• MUST: Measure reliably (disable extensions that skew runtime)
• MUST: Track and minimize re-renders (React DevTools/React Scan)
• MUST: Profile with CPU/network throttling
• MUST: Batch layout reads/writes; avoid reflows/repaints
• MUST: Mutations complete in <500ms
• SHOULD: Prefer uncontrolled inputs; make controlled loops cheap
• MUST: Virtualize large lists (virtua) or content-visibility: auto
• MUST: Preload only above-the-fold images; lazy-load rest
• MUST: Prevent CLS from images (explicit dimensions)
• SHOULD: <link rel="preconnect"> for asset/CDN domains
• SHOULD: Preload critical fonts; subset via unicode-range
• SHOULD: Move expensive work to Web Workers

Design

• SHOULD: Layered shadows (ambient + direct)
• SHOULD: Crisp edges via semi-transparent borders + shadows
• SHOULD: Nested radii: child <= parent; concentric
• SHOULD: Hue consistency: tint borders/shadows/text toward bg hue
• MUST: Accessible charts (color-blind-friendly palettes)
• MUST: Increase contrast on :hover/:active/:focus
• SHOULD: Set <meta name="theme-color"> to match page background
• MUST: Set color-scheme: dark on <html> in dark themes
• MUST: On Windows, set explicit background-color and color on <select>
• SHOULD: Avoid gradient banding (use masks when needed)

Common Violations

Blocking paste

// Bad
<input => e.preventDefault()} />

// Good
<input type="email" autoComplete="email" />

Non-semantic button

// Bad
<div me</div>

// Good
<button me</button>

Windows select dark mode

// Bad
<select><option>Option 1</option></select>

// Good
<select className="bg-white dark:bg-gray-900 text-black dark:text-white">
  <option>Option 1</option>
</select>

References

• WAI-ARIA APG Patterns
• APCA Contrast Calculator
• nuqs - URL State Management
• virtua - List Virtualization