What you need to know
Specificity decides which matching selector wins when declarations conflict. Excessively specific selectors make a codebase harder to override, while source order and cascade layers also affect the final result.
How to apply it
Prefer simple class selectors, keep component styles near their component, and inspect the browser's computed styles when a rule does not apply. Use a consistent design token or utility convention for shared values.
Common mistake to avoid
Avoid repeatedly adding IDs or !important to defeat earlier rules. Reduce the original conflict or define a clear layer for intentional overrides.