[css-nav-1] Modify the example of spatial-navigation-function

 Modify the example of `spatial-navigation-function` as viewing the behavior of it more clearly

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -1579,7 +1579,7 @@ NOTE: These values are negotiated with the users' preferences which seems natura
         <figcaption>Moving focus from "A" to one of the candidate elements</figcaption>
     </figure>
 
-    Let the element which contains "A", "B", "C" and "D" is the <a>spatial navigation container</a>.
+    Let the element which contains "A", "B" and "C" is the <a>spatial navigation container</a>.
 
     When the user presses the down arrow key,
     if <code highlight=css>normal</code> value is given to <code highlight=css>spatial-navigation-function</code> of the element, the focus will move to "B".
@@ -1693,7 +1693,7 @@ Answers are provided below.
   <dd>No.
 
   <dt>How should this specification work in the context of a user agent’s "incognito" mode?
-  <dd>No Difference is expected.
+  <dd>No Difference.
 
   <dt>Does this specification persist data to a user’s local device?
   <dd>No.