Fix some details in the description

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -1267,16 +1267,17 @@ the proper spatial navigation behavior.
 <dl dfn-for=spatial-navigation-action dfn-type=value>
     <dt><dfn>auto</dfn>
     <dd>If the element is a <a>scroll container</a>,
-        then directional input moves the focus to the candidates in the viewport.
+        then directional input moves the focus to the candidates in the optimal viewing region.
         When there isn't any visible candidate, then the container scrolls.
-
-        Else, the focus moves to the candidates in the viewport.
+        
+        Otherwise, the focus moves to the candidates in the viewport.
 
     <dt><dfn>focus</dfn>
-    <dd>The directional input moves the focus to all candidates inside a scroll container. The user cannot manually scroll the container.
+    <dd>The directional input moves the focus to all candidates inside a scroll container. The container <a>cannot be scrolled manually</a>.
 
-    NOTE: If the 'focus' value is given to 'spatial-navigation-action', 'navnotarget' event occurs 
-    when there isn’t any visible candidate in the spatial navigation container no matter what it can be scrolled more or not.
+    NOTE: If the 'focus' value is given to 'spatial-navigation-action', 
+    <a event>navnotarget</a> event occurs when there isn’t any visible candidate in the given direction within the viewport of 
+    the <a>spatial navigation container</a> even through the container can be scrolled more.
 
     <dt><dfn>scroll</dfn>
     <dd>If the element is a <a>scroll container</a>,
@@ -1286,13 +1287,13 @@ the proper spatial navigation behavior.
 </dl>
 
 <div class=example>
-In this example, a scrollable container is specified with `spatial-navigation-action: focus`.
+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.
 
     <figure>
         <img alt="" src="images/spatnav-action.png" style="width: 500px;"/>
-        <figcaption>Moving focus to "Box 3" from "Box 2" without manually scrolling</figcaption>
+        <figcaption>Moving focus from "Box 2" to "Box 3" without manually scrolling</figcaption>
     </figure>
 
     <pre><code highlight=markup>