A selector's specificity is represented by concatenating three numbers: a-b-c (in a number system with a large base), which are calculated as follows:
a = the count of ID selectors in the selector
b = the count of class selectors, attributes selectors, and pseudo-classes in the selector
c = the count of type selectors and pseudo-elements in the selector
ignore the universal selector
Selectors inside the negation pseudo-class are counted like any other, but the negation itself does not count as a pseudo-class.
Examples:
* /* a=0 b=0 c=0 -> specificity = 0 */
LI /* a=0 b=0 c=1 -> specificity = 1 */
UL LI /* a=0 b=0 c=2 -> specificity = 2 */
UL OL+LI /* a=0 b=0 c=3 -> specificity = 3 */
H1 + *[REL=up] /* a=0 b=1 c=1 -> specificity = 11 */
UL OL LI.red /* a=0 b=1 c=3 -> specificity = 13 */
LI.red.level /* a=0 b=2 c=1 -> specificity = 21 */
#x34y /* a=1 b=0 c=0 -> specificity = 100 */
#s12:not(FOO) /* a=1 b=0 c=1 -> specificity = 101 */Note: Repeated occurrences of the same simple selector are allowed and do increase specificity.