Bikeshed-added 5 tests and improved 1 inter-spec link

Author: TalbotG

css-pseudo-4/Overview.bs

@@ -592,6 +592,10 @@ Cascading and Per-Element Highlight Styles</h3>
   of its <a>originating element</a>'s parent element
   (regardless of whether that property is an <a>inherited property</a>).
 
+    <wpt>
+    css/css-pseudo/cascade-highlight-004.html
+    </wpt>
+
   <div class="example">
     For example, if the following rules were applied:
     <pre>
@@ -608,6 +612,10 @@ Cascading and Per-Element Highlight Styles</h3>
     and orange text inside it.
   </div>
 
+    <wpt>
+    css/css-pseudo/cascade-highlight-001.html
+    </wpt>
+
   <p class="advisement">
   Authors wanting multiple selections styles should use
   <strong>'':root::selection''</strong>
@@ -638,6 +646,11 @@ Cascading and Per-Element Highlight Styles</h3>
     </pre>
   </div>
 
+    <wpt>
+    css/css-pseudo/cascade-highlight-002.html
+    </wpt>
+
+
   The UA should use the OS-default highlight colors for ''::selection''
   when neither 'color' nor 'background-color' has been specified by the author.
 
@@ -655,12 +668,17 @@ Painting the Highlight</h3>
   over the corresponding portion of the <a>highlight overlay</a>,
   painting it
   immediately below any positioned descendants
-  (i.e. just before step 8 in <a href="https://www.w3.org/TR/CSS21/zindex.html">CSS2.1&sect;E.2</a>).
+  (i.e. just before step 8 in <a href="https://www.w3.org/TR/CSS22/zindex.html#painting-order">CSS2.2&sect;E.2</a>).
   <!-- Its outline, if any, is painted immediately over its background. -->
   The ''::selection'' overlay is drawn
   over the ''::spelling-error'' overlay
   which is drawn over the ''::grammar-error'' overlay.
 
+  <wpt>
+  css/css-pseudo/highlight-z-index-001.html
+  css/css-pseudo/highlight-z-index-002.html
+  </wpt>
+
   A <a>highlight pseudo-element</a>
   also suppresses the drawing of any selected text
   (and any text decorations applied to that text).