Problem:
- The .flip-card-container in the global stylesheet uses the perspective property. This value cannot be adjusted via the GUI or the designOption.json.
- If no image is set on the front side, a gray mouseover overlay appears. Its color and visibility cannot currently be changed in the GUI or the designOption.json.

Suggestion:
- Make the perspective value adjustable in both the GUI and the designOption.json.
- Allow configuring the color and behavior (show/hide) of the mouseover overlay in the GUI and designOption.json.