The CSSStyleRule interface represents a single CSS style rule.
Inherits properties from its ancestors CSSGroupingRule and CSSRule.
CSSStyleRule.selectorTextReturns the textual representation of the selector for this rule, e.g., "h1, h2".
CSSStyleRule.style Read onlyReturns the CSSStyleProperties object for the rule, which represents its styles.
CSSStyleRule.styleMap Read onlyReturns a StylePropertyMap object which provides access to the rule's property-value pairs.
Inherits methods from its ancestors CSSGroupingRule and CSSRule.
The CSS below defines the style rule for the h1 selector, which is represented in code by a CSSStyleRule instance.
h1 {
color: pink;
}Assuming the above style rule is the first rule in the document, it will be the first CSSRule returned by document.styleSheets[0].cssRules. myRules[0].style returns a CSSStyleProperties object representing the declarations defined for h1.
let myRules = document.styleSheets[0].cssRules;
console.log(myRules[0]); // a CSSStyleRule representing the h1.