What is CSS specificity?

CSS specificity is the algorithm browsers use to determine which CSS rule wins when multiple rules target the same element and property. It is calculated as a three-part score: [ID count, Class/Attribute/Pseudo-class count, Element/Pseudo-element count]. For example, #nav .link:hover has specificity (1, 2, 0). Higher specificity always wins, regardless of source order — only when specificity ties does the later rule win. Inline styles (style="") override all external/internal CSS. The !important declaration overrides all specificity rules and should be avoided except as a last resort. Understanding specificity is essential for debugging unexpected style overrides.