The parentStyleSheet property of the CSSRule interface returns the StyleSheet object in which the current rule is defined. 
 The parentStyleSheet property of the CSSRule interface returns the StyleSheet object in which the current rule is defined. 
A StyleSheet object.
js
const docRules = document.styleSheets[0].cssRules; console.log(docRules[0].parentStyleSheet == document.styleSheets[0]); // returns true
| Specification | 
|---|
| CSS Object Model (CSSOM)  # dom-cssrule-parentstylesheet  | 
| Desktop | Mobile | |||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Chrome | Edge | Firefox | Internet Explorer | Opera | Safari | WebView Android | Chrome Android | Firefox for Android | Opera Android | Safari on IOS | Samsung Internet | |
parentStyleSheet | 
1 | 12 | 1 | 9 | ≤12.1 | 1 | 4.4 | 18 | 4 | ≤12.1 | 1 | 1.0 | 
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    https://developer.mozilla.org/en-US/docs/Web/API/CSSRule/parentStyleSheet