Debugging CSS can be challenging because the language does not throw errors when issues arise, making it difficult to identify why an application doesn't appear as expected. To effectively debug CSS, it is crucial to isolate the styles affecting an element, often using tools like Replay's inspector to view applied styles, their sources, and any overridden styles. Understanding CSS specificity is essential as it determines the order of importance for style rules, affecting which styles are applied to an element. In modern frameworks like React, CSS classes are often applied dynamically based on application logic, which can complicate tracing their source. Inspecting React props and understanding the cascade order in CSS can aid in resolving these complexities. Additionally, concepts like the box model, layout properties, media queries, and browser compatibility are vital areas to explore when troubleshooting CSS issues, as they influence spacing, responsiveness, and appearance across different devices and browsers. Resources such as Smashing Magazine, MDN Web Docs, and CSS-Tricks offer further guidance on common CSS debugging challenges.