The read-only inherits property of the CSSPropertyRule interface returns the inherit flag of the custom property registration represented by the @property rule, a boolean describing whether or not the property inherits by default.

A boolean.

This stylesheet contains a single @property rule. The first CSSRule returned will be a CSSPropertyRule representing this rule. The inherits property returns the boolean false, this being the value of the inherits property in the CSS.

@property --property-name {
  syntax: "<color>";
  inherits: false;
  initial-value: #c0ffee;
}

let myRules = document.styleSheets[0].cssRules;
console.log(myRules[0].inherits); //returns false