Returns the specificity (>=0) of the match with the selector string or -1 if there is no match.
A selector's specificity is calculated as follows:
|1.||Count the number of ID selectors in the selector (= a)|
|2.||Count the number of class selectors, attributes selectors, and pseudo-classes in the selector (= b)|
|3.||Count the number of type selectors and pseudo-elements in the selector (= c)|
|4.||Ignore the universal selector|
|5.||Selectors inside the negation pseudo-class are counted like any other, but the negation itself does not count as a pseudo-class.|