A CSS rule appears correct but does not win, or unexpectedly affects descendants. How would you debug the cascade?

The durable fix is usually predictable style ownership: deliberate layers, low-specificity component selectors, explicit tokens, and limited escape hatches. I avoid routine !important because it transfers the conflict to a harder level, though it can be justified in a controlled utility or user override layer. Visual regression tests cover critical states, but they complement rather than replace an understandable cascade. For third-party styles, I isolate the integration or place its overrides in a named layer instead of escalating selectors across the application.