Use CSS media queries to apply different styles for different devices and screen sizes, making your site responsive.
Media queries are a core feature of CSS3 that allow you to tailor your web page's presentation to a specific range of output devices without changing the content itself. They are the fundamental building block of responsive web design. A media query consists of a media type (e.g., `screen`, `print`) and one or more expressions involving media features, such as screen width, height, or orientation. The most common use case is applying different CSS styles based on the viewport width. This allows you to create layouts that adapt to various screen sizes, from small mobile phones to large desktop monitors. The syntax involves the `@media` rule. For example, you can define a 'breakpoint' at 768 pixels. Any CSS rules inside `@media (min-width: 768px) { ... }` will only apply when the browser's viewport is 768 pixels wide or wider. A 'mobile-first' approach is a common best practice. With this strategy, you write your base CSS for mobile devices first, and then use media queries with `min-width` to add styles for larger screens. This ensures that mobile users download a smaller, more optimized stylesheet. You can create multiple breakpoints to adjust your layout for tablets, laptops, and large screens, ensuring an optimal user experience across all devices. This could mean changing a two-column layout to a single-column layout, increasing font sizes, or hiding non-essential elements on smaller screens.