Remove the border-radius from the dataTable of the MultiSite plugin for PleineLune

plugins/PleineLune/stylesheets/_dataTable.less

@@ -177,4 +177,10 @@ table.dataTable tr.subDataTable:hover > td .dataTableRowActions {
 .tableConfiguration div.configItem:hover span.action {
   text-decoration: underline;
   color: @theme-color-text-focus;
+}
+
+/* MultiSites */
+#mt thead *:first-child,
+#mt thead *:first-child {
+  border-radius: 0;
 }
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