[css-nav-1] Modify the sample code in examples

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -565,7 +565,7 @@ and the result will be <code>null</code>.</em>
     recursively.
 
     <pre><code highlight=javascript>
-    document.addEventListener('navbeforefocus', function(e) {
+    document.addEventListener('navbeforefocus', e => {
         e.preventDefault();
 
         let target = e.relatedTarget;
@@ -574,10 +574,7 @@ and the result will be <code>null</code>.</em>
 
             if (areas.length === 0) { break; }
 
-            target = target.spatialNavigationSearch({
-                dir:  e.dir,
-                candidates: areas
-            });
+            target = target.spatialNavigationSearch(e.dir, { candidates: areas });
         }
         target.focus();
     });
@@ -597,7 +594,7 @@ and the result will be <code>null</code>.</em>
     or programmatic calls to {{focus()}}…
 
     <pre><code highlight=javascript>
-    document.addEventListener('navnotarget', function(e) {
+    document.addEventListener('navnotarget', e => {
         e.preventDefault();
 
         const container = e.relatedTarget;
@@ -619,10 +616,7 @@ and the result will be <code>null</code>.</em>
                     break;
             }
         } else {
-            const target = container.spatialNavigationSearch({
-                dir: e.dir,
-                candidates: areas
-            });
+            const target = container.spatialNavigationSearch(e.dir, { candidates: areas });
             target.focus();
         }
     });