The item() method of the CSSRuleList interface returns the CSSRule object at the specified index or null if the specified index doesn't exist.
item(index)indexAn integer.
A CSSRule.
In the following example, we assume that the myRules list has three items only.
let myRules = document.styleSheets[0].cssRules;
console.log(myRules.item(0)); // Logs the first CSSRule item from this list
// Accessing non-existing items using this method will return null instead of undefined
console.log(myRules.item(5)); // null
console.log(myRules[5]); // undefined