Frontend Design: Build Polished Web UIs

You are creating frontend code (HTML, CSS, JavaScript). Follow these design principles to produce visually polished, production-quality results.

Design Principles

Layout & Spacing

• Use consistent spacing scales (4px, 8px, 12px, 16px, 24px, 32px, 48px, 64px)
• Add generous whitespace — don't crowd elements
• Use CSS Grid or Flexbox for layout, never tables for layout
• Ensure content has a max-width (960-1200px) with auto margins for readability

Typography

• Use a clean sans-serif system font stack: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif
• Establish clear hierarchy: 1 large heading, supportive subheading, readable body text (16px+)
• Line-height: 1.5-1.7 for body, 1.1-1.3 for headings
• Limit line length to ~65-75 characters for readability

Color

• Start with a neutral palette (grays) and one accent color
• Ensure WCAG AA contrast ratios (4.5:1 for text)
• Use color purposefully: primary action, success, warning, error
• Dark mode: use dark grays (#1a1a2e, #16213e) not pure black

Components

• Buttons: clear hierarchy (primary filled, secondary outlined, text-only for tertiary)
• Cards: subtle borders or shadows, rounded corners (8-12px), consistent padding
• Forms: large touch targets (44px+), clear labels, visible focus states
• Modals: backdrop overlay, centered, max-width, close button

Interactions & Animation

• Add hover states for interactive elements (subtle background change or scale)
• Use CSS transitions (150-300ms ease) for state changes
• Animate entrances with subtle fade-in or slide-up
• Use transform and opacity for performant animations

Responsive Design

• Mobile-first approach: design for small screens, enhance for larger
• Use relative units (rem, %, vw/vh) over fixed px where appropriate
• Test breakpoints: 480px, 768px, 1024px, 1280px
• Touch-friendly: minimum 44x44px tap targets

For Games & Interactive Projects

When building games or interactive experiences:

• Use <canvas> or DOM-based rendering as appropriate for the complexity
• Implement proper game loop with requestAnimationFrame
• Handle keyboard/mouse/touch input cleanly
• Add visual feedback for user actions (particles, screen shake, color flash)
• Include a start screen, HUD/score display, and game over state
• Use sprite-based or procedural graphics — avoid placeholder rectangles
• Add sound effects where appropriate using Web Audio API
• Target 60fps — optimize render loops

For Single-File Projects

When creating everything in one HTML file:

• Inline CSS in <style> and JS in <script>
• Use modern ES6+ JavaScript (no build tools needed)
• Structure code with clear sections: styles, markup, logic
• Result should be immediately openable in a browser

Output Guidelines

• Write complete, runnable code — no placeholders or TODOs
• Include all assets inline (SVG icons, CSS gradients for backgrounds)
• Add a favicon using an inline SVG data URI
• Make it immediately impressive when opened in a browser