Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.
rules is a deprecated legacy property of the CSSStyleSheet interface. Functionally identical to the preferred cssRules property, it provides access to a live-updating list of the CSS rules comprising the stylesheet.
Note: As a legacy property, you should not use rules and should instead use the preferred cssRules. While rules is unlikely to be removed soon, its availability is not as widespread and using it will result in compatibility problems for your site or app.