Limit blue background to th in thead or tfoot

Author: NicolaSaunders

assets-src/styles/sass/30-base/_tables.scss

@@ -34,9 +34,13 @@ table caption {
 }
 
 th {
+    vertical-align: bottom;
+}
+
+thead th,
+tfoot th {
     background-color: $deep-blue;
     color: $white;
-    vertical-align: bottom;
 }
 
 td {

design-system-templates/components/table.html.twig

@@ -4,9 +4,9 @@
 	</caption>
 	<thead>
 	<tr>
-		<td></td>
-		<th scope="col">Column header 1</th>
+        <th scope="col">Column header 1</th>
 		<th scope="col">Column header 2</th>
+		<th scope="col">Column header 3</th>
 	</tr>
 	</thead>
 	<tbody>

public/dist/assets/styles/core.css

@@ -1939,9 +1939,13 @@ table caption {
 }
 
 th {
+  vertical-align: bottom;
+}
+
+thead th,
+tfoot th {
   background-color: #024488;
   color: #fff;
-  vertical-align: bottom;
 }
 
 td {