Fix for table headings.

publication/editor-blocks.css

@@ -505,8 +505,12 @@
 }
 
 .wp-block-freeform.block-library-rich-text__tinymce table th {
+	border: 0;
+	background: #eee;
 	border-bottom: 1px solid #ddd;
 	padding: 6px;
+	font-weight: bold;
+	text-transform: uppercase;
 }
 
 .wp-block-freeform.block-library-rich-text__tinymce table tr:nth-of-type(even) {
@@ -636,8 +640,11 @@
 
 .editor-block-list__block table.wp-block-table th {
 	border: 0;
+	background: #eee;
 	border-bottom: 1px solid #ddd;
 	padding: 6px;
+	font-weight: bold;
+	text-transform: uppercase;
 }
 
 .editor-block-list__block table.wp-block-table tr:nth-of-type(even) {