Chore: revise table styles (#521)

use the 'data' class, instead of the previous 'simple' class, to give tables some level of visual layout styling

Author: scottaohara

index.html

@@ -491,7 +491,7 @@ <h2 id="docconformance">
         While it is conforming to use [[[dpub-aria-1.0]]] `role` values as outlined in the following table, the current support for 
         exposing the semantics of these values to users of assistive technology is close to non-existent.
       </p>
-      <table class="simple">
+      <table class="data">
         <caption>
           Rules of ARIA attribute usage by HTML element
         </caption>
@@ -3594,7 +3594,7 @@ <h3 id="docconformance-attr">
           requirements for using the `aria-*` attributes that supply the same
           <a>implicit ARIA semantics</a>.
         </p>
-        <table class="simple">
+        <table class="data">
           <caption>
             Rules of ARIA attribute usage by HTML feature
           </caption>
@@ -4007,7 +4007,7 @@ <h2>
       Additionally, there are certain roles which [[[wai-aria-1.2]]] has specified specific requirements for their allowed descendants. These have been identified in column 3 (Descendant allowances) by indicating to "Refer to the 'Required Owned Elements'" for those particular roles.
     </p>
 
-    <table id="aria-table" class="simple">
+    <table id="aria-table" class="data">
       <caption>
         Allowed descendants of ARIA roles
       </caption>