Fix errors reported by the markup validator

Used tool: https://validator.w3.org/

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -486,7 +486,7 @@ Note: the {{focusableAreas()}} and {{getSpatialNavigationContainer()}} methods a
 :   <dfn method for=Element lt="focusableAreas(option)">focusableAreas(<var>option</var>)</dfn>
 ::  Follows these steps:
 1. Let <var>visibleOnly</var> be <code>false</code>
-    if <var>option</var> is present and it's value is equal to <code>'all'</code>,
+    if <var>option</var> is present and its value is equal to <code>'all'</code>,
     or <code>true</code> otherwise.
 2. Let <var>areas</var> be the result of <a>finding focusable areas</a> within the element with the <var>visibleOnly</var>.
 3. Let <var>anchors</var> be a <a for=list>clone</a> of <var>areas</var>,
@@ -1294,7 +1294,7 @@ Note: In addition, as per [[#grouping]], the viewport of a <a for="/">browsing c
 
         /* For browsers that don't support grid */
         #example-cal table {
-            display:inline-table
+            display:inline-table;
             vertical-align: middle;
         }
         </style>
@@ -1456,7 +1456,7 @@ Answers are provided below.
   <dt>How should this specification work in the context of a user agent’s "incognito" mode?
   <dd>No Difference is expected.
 
-  <dt>Does this specification persist data to a user’s local device?<Paste>
+  <dt>Does this specification persist data to a user’s local device?
   <dd>No.
 
   <dt>Does this specification have a "Security Considerations" and "Privacy Considerations" section?