[css-nav-1] Modify Example8

Update the relatedTarget info of focus and focusin event

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -798,13 +798,13 @@ the <a spec=html for="/">origin</a> of the [=active document=] of the [=top-leve
                 <td>4
                 <td>focusin
                 <td><code>#box3</code>
-                <td>N/A
+                <td><code>#box2</code>
                 <td>Sent before the target element receives focus.
             <tr>
                 <td>5
                 <td>focus
                 <td><code>#box3</code>
-                <td>N/A
+                <td><code>#box2</code>
                 <td>Sent after the target element receives focus.
         </tbody>
     </table>