put the diagram center

packages/remark-drawio-plugin/src/components/DrawioViewer.module.scss

@@ -2,4 +2,11 @@
   margin: 20px 0;
   border: 1px solid transparent;
   border-radius: 4px;
+
+  .geDiagramContainer {
+    // centering
+    margin-right: auto;
+    margin-left: auto;
+  }
+
 }