Baseline UI

Baseline UI

Enforces an opinionated UI baseline to prevent AI-generated interface slop. Includes responsive design patterns for mobile-first development.

How to use

• /baseline-ui Apply these constraints to any UI work in this conversation.

• /baseline-ui <file> Review the file against all constraints below and output:

  • violations (quote the exact line/snippet)
  • why it matters (1 short sentence)
  • a concrete fix (code-level suggestion)

When to use

Reference these guidelines when:

• building UI components in Tailwind CSS
• reviewing CSS utilities or styling React views
• enforcing design consistency across a project
• building responsive layouts for mobile/tablet/desktop
• implementing fluid typography or responsive navigation
• using CSS Grid, Flexbox, or container queries for layouts
• testing across screen sizes

When NOT to use

Do NOT apply this skill when:

• the project uses a different CSS framework (Bootstrap, vanilla CSS) — adapt principles but not Tailwind-specific rules
• the task is purely creative/experimental design (use frontend-design skill)
• the task is about animation performance debugging (use fixing-motion-performance skill)

Stack

• MUST use Tailwind CSS defaults unless custom values already exist or are explicitly requested
• MUST use motion/react (formerly framer-motion) when JavaScript animation is required
• SHOULD use tw-animate-css for entrance and micro-animations in Tailwind CSS
• MUST use cn utility (clsx + tailwind-merge) for class logic

Components

• MUST use accessible component primitives for anything with keyboard or focus behavior (Base UI, React Aria, Radix)
• MUST use the project's existing component primitives first
• NEVER mix primitive systems within the same interaction surface
• SHOULD prefer Base UI for new primitives if compatible with the stack
• MUST add an aria-label to icon-only buttons
• NEVER rebuild keyboard or focus behavior by hand unless explicitly requested

Interaction

• MUST use an AlertDialog for destructive or irreversible actions
• SHOULD use structural skeletons for loading states
• NEVER use h-screen, use h-dvh
• MUST respect safe-area-inset for fixed elements
• MUST show errors next to where the action happens
• NEVER block paste in input or textarea elements

Animation

• NEVER add animation unless it is explicitly requested
• MUST animate only compositor props (transform, opacity)
• NEVER animate layout properties (width, height, top, left, margin, padding)
• SHOULD avoid animating paint properties (background, color) except for small, local UI (text, icons)
• SHOULD use ease-out on entrance
• NEVER exceed 200ms for interaction feedback
• MUST pause looping animations when off-screen
• SHOULD respect prefers-reduced-motion
• NEVER introduce custom easing curves unless explicitly requested
• SHOULD avoid animating large images or full-screen surfaces

Typography

• MUST use text-balance for headings and text-pretty for body/paragraphs
• MUST use tabular-nums for data
• SHOULD use truncate or line-clamp for dense UI
• NEVER modify letter-spacing (tracking-*) unless explicitly requested

Layout

• MUST use a fixed z-index scale (no arbitrary z-*)
• SHOULD use size-* for square elements instead of w-* + h-*

Performance

• NEVER animate large blur() or backdrop-filter surfaces
• NEVER apply will-change outside an active animation
• NEVER use useEffect for anything that can be expressed as render logic

Design

• NEVER use gradients unless explicitly requested
• NEVER use purple or multicolor gradients
• NEVER use glow effects as primary affordances
• SHOULD use Tailwind CSS default shadow scale unless explicitly requested
• MUST give empty states one clear next action
• SHOULD limit accent color usage to one per view
• SHOULD use existing theme or Tailwind CSS color tokens before introducing new ones

Responsive Design

Mobile-First Methodology

Start with mobile styles, progressively enhance for larger screens.

/* Mobile-first: base styles ARE mobile styles */
.container {
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
}

/* Tablet and up */
@media (min-width: 768px) {
  .container {
    padding: 2rem;
    flex-direction: row;
    gap: 2rem;
  }
}

/* Desktop */
@media (min-width: 1024px) {
  .container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 3rem;
  }
}

Why mobile-first: Forces content prioritization, smaller CSS payload for mobile, progressive enhancement is more robust than graceful degradation.

Breakpoint System (Tailwind)

Prefer content-based breakpoints over device-based when possible:

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(300px, 100%), 1fr));
  gap: 1.5rem;
}
/* No media queries needed — grid adapts automatically */

Shadcn-UI Responsive Patterns

<div className="grid grid-cols-1 md:grid-cols-2 lg:grid-cols-3 gap-4">
  <Card className="p-4 md:p-6">
    <CardTitle className="text-lg md:text-xl lg:text-2xl">Title</CardTitle>
    <CardContent className="text-sm md:text-base">Content</CardContent>
  </Card>
</div>

Fluid Typography

:root {
  --text-xs: clamp(0.75rem, 0.7rem + 0.25vw, 0.875rem);
  --text-sm: clamp(0.875rem, 0.825rem + 0.25vw, 1rem);
  --text-base: clamp(1rem, 0.95rem + 0.25vw, 1.125rem);
  --text-lg: clamp(1.125rem, 1rem + 0.5vw, 1.25rem);
  --text-xl: clamp(1.25rem, 1.1rem + 0.75vw, 1.5rem);
  --text-2xl: clamp(1.5rem, 1.2rem + 1.5vw, 2rem);
  --text-3xl: clamp(1.875rem, 1.4rem + 2.25vw, 2.5rem);
  --text-4xl: clamp(2.25rem, 1.5rem + 3.5vw, 3.5rem);

  --space-xs: clamp(0.25rem, 0.2rem + 0.25vw, 0.5rem);
  --space-sm: clamp(0.5rem, 0.4rem + 0.5vw, 0.75rem);
  --space-md: clamp(1rem, 0.8rem + 1vw, 1.5rem);
  --space-lg: clamp(1.5rem, 1.2rem + 1.5vw, 2.5rem);
  --space-xl: clamp(2rem, 1.5rem + 2.5vw, 4rem);
}

Container Queries

.card-container {
  container-type: inline-size;
  container-name: card;
}

@container card (min-width: 400px) {
  .card-body {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
  }
}

@container card (min-width: 600px) {
  .card-body {
    grid-template-columns: 1fr 2fr;
  }
}

Responsive Images

<picture>
  <source media="(min-width: 1024px)" srcset="hero-desktop.webp" />
  <source media="(min-width: 640px)" srcset="hero-tablet.webp" />
  <img src="hero-mobile.webp" alt="Hero image" loading="lazy" />
</picture>

<img
  srcset="photo-400.webp 400w, photo-800.webp 800w, photo-1200.webp 1200w"
  sizes="(min-width: 1024px) 50vw, (min-width: 640px) 75vw, 100vw"
  src="photo-800.webp"
  alt="Photo"
  loading="lazy"
  decoding="async"
/>

Responsive Navigation

Hamburger menu (mobile → desktop):

.nav-links { display: none; }
.nav-toggle { display: block; }

@media (min-width: 768px) {
  .nav-links { display: flex; gap: 1.5rem; }
  .nav-toggle { display: none; }
}

Bottom tab bar (mobile only):

.bottom-nav {
  position: fixed;
  bottom: 0;
  left: 0;
  right: 0;
  display: flex;
  justify-content: space-around;
  padding: 0.5rem;
}

@media (min-width: 768px) {
  .bottom-nav { display: none; }
}

Responsive Tables

/* Horizontal scroll */
.table-wrapper {
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}

/* Card layout on mobile */
@media (max-width: 640px) {
  table, thead, tbody, th, td, tr { display: block; }
  thead { display: none; }
  td {
    position: relative;
    padding-left: 50%;
  }
  td::before {
    content: attr(data-label);
    position: absolute;
    left: 0.5rem;
    font-weight: 600;
  }
}

Touch-Friendly Design

• 44x44px minimum touch target (Apple HIG)
• 48x48dp minimum touch target (Material Design)
• 8px minimum spacing between touch targets

.btn {
  min-height: 44px;
  min-width: 44px;
  padding: 0.75rem 1.5rem;
}

.icon-btn {
  position: relative;
}
.icon-btn::after {
  content: "";
  position: absolute;
  inset: -8px; /* Expand tap area */
}

Dark Mode + Responsive

:root {
  --bg: #ffffff;
  --text: #1a1a1a;
  --card-bg: #f9fafb;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0a0a0a;
    --text: #f5f5f5;
    --card-bg: #1a1a1a;
  }
}

Responsive Checklist

• Test at all Tailwind breakpoints (640, 768, 1024, 1280, 1536px)
• Test landscape orientation on mobile
• Verify touch targets are 44px+ on mobile
• Check text readability at all sizes
• Verify images don't overflow containers
• Test navigation collapse/expand
• Check form inputs are usable on mobile
• Verify no horizontal scroll at any breakpoint
• Test with browser zoom (200%, 400%)
• Check prefers-reduced-motion support
• Use webapp-testing skill for Playwright viewport testing

Cross-references

• frontend-design skill: Creative UI design, bold aesthetics
• fixing-accessibility skill: ARIA, keyboard nav, WCAG
• fixing-motion-performance skill: Animation performance debugging
• ui-ux-pro-max skill: 50+ styles, design system generation
• webapp-testing skill: Playwright browser testing across viewports
• FRONTEND_PATTERNS.md: Component library patterns reference