What is a key technique for creating a responsive design in CSS?

Implementing media queries is a fundamental technique for creating a responsive design in CSS. Media queries allow you to apply different styles to your web page based on the characteristics of the device displaying it, such as its width, height, orientation, and resolution. This means you can design your website to adapt seamlessly to a variety of screen sizes, from mobile phones to large desktop monitors.

By using media queries, you can specify breakpoints at which your styles will change, allowing you to enhance user experience by ensuring that text, images, and layouts are appropriately sized and arranged. This approach emphasizes a fluid and flexible style, adapting to the user's environment rather than forcing a single fixed layout across all devices. This adaptability is crucial in modern web design, where users access content through many different devices.

In contrast, utilizing fixed dimensions for elements would hinder responsiveness, as it does not allow for adjustments based on the screen size. Using only images in the design fails to address the variability of text sizes and layouts necessary for different devices. Also, setting all text to a single size does not provide the necessary flexibility for readability across various display situations.