responsive-design（响应式设计）

Responsive Design Guidelines

Core Principles

• Write semantic HTML to improve accessibility and SEO
• Use CSS for styling, avoiding inline styles
• Ensure responsive design using media queries and flexible layouts
• Prioritize accessibility by using ARIA roles and attributes
• Design mobile-first, then enhance for larger screens

Mobile-First Approach

Strategy

• Start with styles for the smallest viewport
• Add complexity through progressive enhancement
• Base styles work without media queries
• Media queries add features for larger screens

Benefits

• Forces prioritization of essential content
• Improves performance on mobile devices
• Ensures core functionality works everywhere
• Reduces CSS complexity and specificity issues

/* Base styles for mobile */
.container {
  padding: 1rem;
}

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

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

Flexible Layouts

Flexbox

• Use for one-dimensional layouts (row or column)
• Leverage flex-wrap for responsive wrapping
• Use gap for consistent spacing
• Combine with media queries for layout changes

CSS Grid

• Use for two-dimensional layouts
• Leverage auto-fit and auto-fill for responsive grids
• Use minmax() for flexible track sizing
• Combine fr units with fixed minimums

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1rem;
}

Container Queries

• Style components based on container size, not viewport
• Use for truly reusable components
• Define containers with container-type

Responsive Typography

Fluid Typography

• Use clamp() for responsive font sizes
• Set minimum, preferred, and maximum values
• Avoid text that's too small on mobile or too large on desktop

h1 {
  font-size: clamp(1.5rem, 4vw + 1rem, 3rem);
}

Units

• Use rem for scalable typography
• Base rem on user's browser settings
• Use em for component-relative sizing
• Avoid fixed px values for font sizes

Responsive Images

Srcset and Sizes

• Use srcset for multiple image resolutions
• Use sizes to indicate display size at breakpoints
• Let browser choose optimal image

<img
  src="image-800.jpg"
  srcset="image-400.jpg 400w, image-800.jpg 800w, image-1200.jpg 1200w"
  sizes="(max-width: 600px) 100vw, (max-width: 1000px) 50vw, 800px"
  alt="Description"
>

Picture Element

• Use for art direction (different crops at different sizes)
• Provide fallback with <img> element
• Use media attributes for breakpoint-specific sources

Performance

• Include width and height attributes to prevent layout shift
• Use loading="lazy" for below-fold images
• Consider aspect-ratio CSS property

Media Queries

Common Breakpoints

/* Small phones */
@media (min-width: 320px) { }

/* Large phones */
@media (min-width: 480px) { }

/* Tablets */
@media (min-width: 768px) { }

/* Laptops/Desktops */
@media (min-width: 1024px) { }

/* Large screens */
@media (min-width: 1280px) { }

/* Extra large screens */
@media (min-width: 1536px) { }

Feature Queries

• Use @supports for feature detection
• Provide fallbacks for unsupported features
• Test for specific CSS properties

Preference Queries

• prefers-color-scheme for dark/light mode
• prefers-reduced-motion for animation preferences
• prefers-contrast for contrast preferences

Touch Targets

Sizing

• Minimum 44x44 pixels for touch targets
• Provide adequate spacing between targets
• Consider thumb reach zones on mobile

Interaction

• Don't rely solely on hover states
• Provide touch alternatives for hover interactions
• Use @media (hover: hover) for hover-capable devices

Viewport Configuration

Meta Tag

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

Best Practices

• Always include viewport meta tag
• Don't disable user scaling (avoid user-scalable=no)
• Test with pinch-to-zoom enabled
• Ensure content is usable at 200% zoom

Testing

Tools

• Browser DevTools device emulation
• Real device testing when possible
• Lighthouse for performance audits
• W3C validators for code quality

Checklist

• Test at multiple viewport sizes
• Test landscape and portrait orientations
• Test with touch and mouse input
• Test with keyboard navigation
• Verify images load appropriate sizes
• Check typography readability
• Verify touch targets are adequate
• Test with browser zoom

Performance Considerations

Critical CSS

• Inline critical above-fold CSS
• Defer non-critical stylesheets
• Minimize render-blocking resources

Asset Optimization

• Compress images appropriately
• Use modern formats (WebP, AVIF)
• Lazy load below-fold content
• Consider responsive loading strategies