In the release notes for today’s update, Dave explains that this feature lets you create custom gradient backgrounds for your widgets. For all users, there is a set of special golden gradient themes. Widgetsmith Premium subscribers can access a bunch of other gradient themes, as well as the ability to “edit the gradients however you’d like.”
Once you download the latest version of Widgetsmith from the App Store, you can find the new gradient themes when creating a widget under the “Themes” section of the editor. You can tap the “Customize Theme” button at the bottom to give the gradient your own personal twist.