CSSRule: parentStyleSheet property

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since September 2015.

The parentStyleSheet property of the CSSRule interface returns the StyleSheet object in which the current rule is defined.

const docRules = document.styleSheets[0].cssRules;
console.log(docRules[0].parentStyleSheet == document.styleSheets[0]); // returns true

Specification
CSS Object Model (CSSOM) # dom-cssrule-parentstylesheet

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