Update cross-reference "unclosed node" to "shadow-closed-hidden"

Ref. whatwg/dom@ca0f853

Author: zcorpan

cssom-view/Overview.bs

@@ -1376,8 +1376,8 @@ The <dfn attribute for=HTMLElement>offsetParent</dfn> attribute must return the
     * The element is <a>the HTML <code>body</code> element</a>.
     * The element's computed value of the 'position' property is ''position/fixed''.
 1. Let <var>ancestor</var> be the parent of the element in the <a>flat tree</a> and repeat these substeps:
-    1. If <var>ancestor</var> is not an <a lt="unclosed node">unclosed</a> element of the element and its computed value of the 'position' property is ''position/fixed'', terminate this algorithm and return null.
-    1. If <var>ancestor</var> is an <a lt="unclosed node">unclosed</a> element of the element and satisfies at least one of the following, terminate this algorithm and return <var>ancestor</var>.
+    1. If <var>ancestor</var> is <a>closed-shadow-hidden</a> from the element and its computed value of the 'position' property is ''position/fixed'', terminate this algorithm and return null.
+    1. If <var>ancestor</var> is not <a>closed-shadow-hidden</a> from the element and satisfies at least one of the following, terminate this algorithm and return <var>ancestor</var>.
         * The computed value of the 'position' property is not ''static''.
         * It is <a>the HTML <code>body</code> element</a>.
         * The computed value of the 'position' property of the element is ''static'' and the ancestor is one of the following <a>HTML elements</a>: <code>td</code>, <code>th</code>, or <code>table</code>.