CSS3 & Responsive Design

Learning Objectives

• Apply CSS3 layout techniques including Flexbox and Grid
• Create responsive designs that work across all devices
• Use CSS media queries effectively
• Implement mobile-first development approach
• Apply CSS frameworks and follow best practices

CSS3 Fundamentals

CSS Box Model:

• Content: The actual content of the element
• Padding: Space between content and border
• Border: Line around padding and content
• Margin: Space outside the border

.box {
width: 200px;
height: 100px;
padding: 20px;
border: 2px solid #333;
margin: 10px;
}

CSS Box Model in Detail

/* Box Model Properties */
.element {
width: 300px;        /* Content width */
height: 200px;       /* Content height */
padding: 20px;       /* Space inside border */
border: 5px solid #000;  /* Border around padding */
margin: 15px;        /* Space outside border */
box-sizing: border-box;  /* Includes padding/border in dimensions */
}

• box-sizing: content-box: Default (width/height = content only)
• box-sizing: border-box: Recommended (width/height includes padding/border)

Flexbox Layout System

Container Properties:

• display: flex: Creates a flex container
• flex-direction: row | row-reverse | column | column-reverse
• justify-content: Aligns items along main axis
• align-items: Aligns items along cross axis

.container {
display: flex;
justify-content: space-between;
align-items: center;
}

CSS Grid Layout

Key Concepts:

• Grid Container: Element with display: grid
• Grid Items: Direct children of grid container
• Grid Lines: Horizontal and vertical lines that create grid
• Grid Tracks: Spaces between grid lines

Media Queries

/* Mobile First Approach */
.container {
width: 100%;
padding: 15px;
}
/* Tablet */
@media (min-width: 768px) {
.container {
max-width: 750px;
margin: 0 auto;
}
}
/* Desktop */
@media (min-width: 1024px) {
.container {
max-width: 1000px;
}
}

Common Breakpoints:

• Mobile: 320px - 767px
• Tablet: 768px - 1023px
• Desktop: 1024px+

Responsive Design Principles

Mobile-First Approach:

1. Start with mobile design (base styles)
2. Use min-width media queries to enhance for larger screens
3. Progressive enhancement for better devices
4. Touch-friendly interface elements

Key Considerations:

• Flexible grid systems
• Scalable images and media
• Readable typography at all sizes
• Intuitive navigation patterns

Viewport Meta Tag

<meta name="viewport" content="width=device-width, initial-scale=1.0">

• width=device-width: Sets viewport width to device width
• initial-scale=1.0: Sets initial zoom level to 100%
• Prevents: Mobile browsers from scaling pages incorrectly

Task 1: Responsive Layout Creation

CSS Frameworks

Popular Options:

• Bootstrap: Most popular CSS framework
• Foundation: Advanced responsive framework
• Bulma: Modern CSS framework based on Flexbox
• Tailwind CSS: Utility-first CSS framework

When to Use:

• Prototyping and rapid development
• Consistent design systems
• Responsive components out of the box

Bootstrap Grid System

<div class="container">
<div class="row">
<div class="col-md-6">Half width on medium+</div>
<div class="col-md-6">Half width on medium+</div>
</div>
</div>

• 12-column grid system
• Responsive breakpoints: xs, sm, md, lg, xl
• Mobile-first approach

Task 2: Cross-Device Testing

Performance Considerations

CSS Performance Tips:

• Minimize CSS specificity conflicts
• Use efficient selectors
• Avoid deep nesting when possible
• Optimize media queries
• Consider critical CSS for above-the-fold content

Responsive Images:

• Use srcset and sizes attributes
• Implement lazy loading
• Consider WebP format for better compression

Accessibility in Layout

Important Considerations:

• Maintain logical reading order
• Ensure sufficient color contrast (4.5:1 minimum)
• Provide focus indicators for keyboard navigation
• Use relative units (em, rem) for scalability
• Test with screen readers

Next Session: JavaScript Fundamentals

• JavaScript basics and data types
• DOM manipulation and event handling
• ES6+ features and best practices
• Debugging techniques
• Browser developer tools

Prepare by reviewing JavaScript fundamentals and practicing basic scripting.