Can you be more specific on what you are trying to achieve? (i.e. an image of the design)
You should be able to make all adjustments using the three tabs that show when you click on the "Expandable root" level (screenshot attached). The second and third tabs are related to the expanded item, while the first one should only be used for an arrow image on the right, set as background.
The borders should be edited with the up/down keys on your keyboard - I'm going to fix them so that they support text input.
Thank you for your feedback - it points out problematic areas in the application.
the Telerik team