fix(plugin): enable ckeditor5's table and table cell properties for responsive table

Closes #3519599

css/responsiveTableStyles.css

@@ -2,3 +2,15 @@ figure.table figcaption.hide-caption,
 figure.table.hide-caption figcaption{
   display: none;
 }
+
+/**
+ * Allow users to specify the background color in all themes.
+ *
+ * (Users can set this using CKEditor 5's optional TableProperties and
+ * TableCellProperties plugins.)
+ */
+.ck tr,
+.ck th,
+.ck td {
+  background-color: transparent;
+}