What is responsive design?

Responsive web design is an approach to web design and development where the layout and content of a site automatically adapt to the screen size of the device, whether it is a desktop, tablet, or smartphone. The goal is to ensure optimal display and usability across all resolutions.

Main principles:

• Fluid Grid: Using relative units of measurement (percentages, em, rem) instead of fixed pixels to define layout element sizes.
• Flexible Images: Images scale proportionally to the size of their container, preventing overflow.
• Media Queries: CSS rules that allow applying different styles depending on device characteristics such as screen width, orientation, resolution.

A typical example of using media queries:

/* Main styles */
.container {
    width: 960px;
    margin: 0 auto;
}

/* Styles for screens smaller than 768px */
@media (max-width: 767px) {
    .container {
        width: 95%;
        padding: 0 10px;
    }
    .column {
        float: none;
        width: 100%;
    }
}

In practice, when testing responsive design, I check:

1. Layout display: No horizontal scrolling, blocks are properly aligned.
2. Text readability: Font sizes should be comfortable on all devices.
3. Navigation: Menus should be accessible and user-friendly (e.g., "burger menu" on mobile).
4. Functionality: All interactive elements (buttons, forms) should work correctly.
5. Performance: Loading time on mobile devices. Using <picture> or srcset for image optimization.

Main advantages of responsive design:

• Single codebase for all devices.
• Improved SEO metrics (Google prefers responsive sites).
• Better user experience.
• Saving time and resources compared to creating separate site versions.

The difference from adaptive design is that the latter uses fixed breakpoints to apply different layouts, whereas responsive design more smoothly adapts to any screen size. These terms are often used as synonyms in the context of development for different devices.