The priority of the rules depends on their relative specificity. Specificity is computed as three numbers, a-b-c (in a number system with a large base). The number of ID building blocks in the selector gives the first number a, the number of classes, pseudo-classes and attributes gives b, and the number of element types gives c.

When two rules give the same specificity number, the order of appearance gives the priority (the last seen overrides previous rules).

Priority is used as follows: first the declarations of all rules that match the same objects are merged, and then the priority is applied only if there is a conflict (same key value) within the merged declaration block.