The system property of the CSSCounterStyleRule interface gets and sets the value of the system descriptor. If the descriptor does not have a value set, this attribute returns an empty string.

A string

The following example shows a @counter-style rule. In JavaScript, myRules[0] is this @counter-style rule, returning system gives us the value "fixed".

@counter-style box-corner {
  system: fixed;
  symbols: ◰ ◳ ◲ ◱;
  suffix: ": ";
}

let myRules = document.styleSheets[0].cssRules;
console.log(myRules[0].system); // "fixed"