How can you set different styles for different screen sizes in CSS?

Using media queries is the method in CSS that allows you to apply different styles based on the characteristics of the device or screen size. Media queries enable responsive design, which means that the layout and styling of a webpage can change dynamically depending on the screen width, height, orientation, and other media features.

When you define a media query in your CSS, you can specify a set of styles that should only be applied when certain conditions are met. For example, you can target devices that have a maximum width of 600 pixels and provide specific styling, ensuring that the content is optimized for smaller screens like smartphones. This helps improve the user experience across a range of devices by ensuring content is accessible and visually appealing, regardless of how it's being viewed.

The other methods in the choices provided do not effectively achieve responsive designs tailored to different screen sizes. Inline styles apply only to individual HTML elements, lacking any adaptable response to screen changes. The font-size property affects text size but does not influence layout or other style aspects based on the screen size. Defining multiple CSS files could separate styles but would require additional effort in managing which file to use based on the screen size, making it a less efficient solution compared to media queries.