Fix use cases in Shadow DOM

Instead of calling document directly we should use getRootNode() to
retrieve the right context.

This fix will ensure dialogs in shadow root's tabbing behavior is
correctly trapped.

Author: muan

index.js

@@ -49,7 +49,7 @@ function restrictTabBehavior(event: KeyboardEvent): void {
   if (elements.length === 0) return
 
   const movement = event.shiftKey ? -1 : 1
-  const currentFocus = dialog.contains(document.activeElement) ? document.activeElement : null
+  const currentFocus = dialog.contains(dialog.getRootNode().activeElement) ? dialog.getRootNode().activeElement : null
   let targetIndex = movement === -1 ? -1 : 0
 
   if (currentFocus) {
@@ -99,8 +99,8 @@ function toggle(event: Event): void {
   if (!(dialog instanceof DetailsDialogElement)) return
 
   if (details.hasAttribute('open')) {
-    if (document.activeElement) {
-      initialized.set(dialog, {details, activeElement: document.activeElement})
+    if (dialog.getRootNode().activeElement) {
+      initialized.set(dialog, {details, activeElement: dialog.getRootNode().activeElement})
     }
 
     autofocus(dialog)