Align the completer with the text in the editor.

packages/completer/style/index.css

@@ -20,7 +20,8 @@
   list-style-type: none;
   overflow: auto;
   padding: 0;
-  margin: 4px 0 0 -4px;
+  /* Position the completer relative to the text editor, align the '.' */
+  margin: 4px 0 0 -30px;
   max-height: calc((10 * var(--jp-private-completer-item-height)) + (2 * var(--jp-border-width)));
   min-height: calc(var(--jp-private-completer-item-height) + (2 * var(--jp-border-width)));
   z-index: 10001;