You can add a search box to your Online Store using an HTML widget:
1. In your Sitebuilder, go to Widgets.
2. Select Popular from the drop-down menu.
3. Drag and drop an HTML widget onto your page. In order for the search box to work, the HTML widget needs to be dropped below the Online Store widget.
4. Copy and paste (use right-click > paste or Ctrl-V to paste) the following code into the HTML editor:
5. When you are done, click Save.
The search box may not display on the page immediately, but to see it in action click the Preview button.