Sortable Table Example: Improve CSS so it works when all columns are …

…sortable (pull #2910)

Fix issue #2904: Ensure that the TH height is sufficient if the table is changed to make all the columns sortable.

content/patterns/table/examples/css/sortable-table.css

@@ -24,7 +24,6 @@ table.sortable th:nth-child(5) {
 }
 
 table.sortable th button {
-  position: absolute;
   padding: 4px;
   margin: 1px;
   font-size: 100%;