To add a widget to your menu, go to Appearance > Menus and add any menu item.

If you wish to add only a Widget and no other content within the item, add a Custom Content item, set the URL to # and the Link Text to a name for your widget item

Open the Bellows Menu Item Settings Panel for your widget item, and click on the Widgets tab. Here you can set up a custom widget area for this menu item. Enter a name for your widget area in the Custom Widget Area setting.

If you would like to hide the link title, you can check the Disable Link setting under the General tab.

Save your menu item settings and the menu (if you have just added a new menu item).

After saving the menu item settings, visit your Widgets screen under Appearance > Widgets.

You will see a new widget area has been added with the custom widget area name you set.

Expand the widget area and drag the widget you’d like to add into that widget area. If you add multiple widgets, they will stack vertically.

Your widget will appear on the front end of the site.

Note that Bellows does not control the styles of your widget, those are controlled by the widget itself; Bellows just provides the container.