In the current version of Forge using a custom UI in a Confluence content action wraps the apps iframe in containers with two separate borders/drop shawo and an unnecessary scrollbar. As far as I can see this must be a change in recent months, as we have an app that uses this and I remember it not behaving like this.
Steps to reproduce:
forge createand select Custom > confluence-content-action as the template
- Build, deploy and install the app on a Confluence instance
- Open the custom UI via the new entry in the Page tools menu
The content that the custom UI produces is either in a proper dialog chrome or on a blank modal blanket and can render its own dialog chrome (old behaviour as far as I remember) .
The Custom UI content is visually shown inside of two containers with a scrollbar even though the content does not exceed the height there at all. The inner of the two borders/drop shadows is set on the iframe that contains the content, so both are outside the control of the app.
Example screenshot of the current behaviour: