Fix the minor mistake

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -1289,7 +1289,7 @@ the proper spatial navigation behavior.
 <div class=example>
 In this example, a scrollable container is specified with <code highlight=css>spatial-navigation-action: focus</code>.
 Inside the container, there is an element which is out of the view within a <a>scrollport</a>.
-Pressing the down arrow key moves the focus directly to it without scrolling manually.
+Pressing the right arrow key moves the focus directly to it without scrolling manually.
 
     <figure>
         <img alt="" src="images/spatnav-action.png" style="width: 500px;"/>