Custom Visual that extends outside of the its container

Hi RyanBentham,

Custom visuals are hosted as sandboxed iframes within a report, and rich HTML is not permitted to overflow the boundaries of the container, due to the restrictions MS have imposed upon this sandbox.

Core visuals are hosted as div elements within the report, and therefore don't have the same issues that we as third-party developers have in this regard.

With custom visuals, you can only exceed the boundaries of the container by using pure HTML form input elements, and not components or controls that are styled using more complex HTML. These elements have limited styling options, but will do what you want if you can accept this as an outcome.

The only supported way to exceed the boundaries of a visual is to use the dialog box API, which was introduced specifically for this limitation, and may be possible to adapt for your situation, but this may create some significant friction with UX, if you need it to serve as the list of options for a dropdown list. 

The alternative is as you've currently observed, and that's to ensure that your users size the visual to leave enough space for the dropdown list to grow into.

Regards,

Daniel