Which use case is appropriate for Chrome DevTools?

The use of Chrome DevTools is particularly well-suited for inspecting CSS on a webpage. This tool provides developers and designers with a robust interface for examining and modifying the current state of a webpage in real-time. When using Chrome DevTools, one can easily view the styles applied to specific elements, modify those styles, and see the results instantly. This feature is invaluable for fine-tuning the look and feel of a webpage, debugging CSS issues, and experimenting with different style rules without altering the underlying code directly.

In contrast, other options listed don't align as closely with the primary functionalities of Chrome DevTools. Creating mobile responsive designs involves a broader set of processes and tools, including design software and frameworks, rather than just inspecting elements. Generating UX prototypes typically requires specialized software that can combine interactive elements with design, which is not the primary function of DevTools. Lastly, building user personas is a user research activity that involves understanding user demographics, behaviors, and needs, and does not utilize the features offered by Chrome DevTools.