To reproduce: 1. Add a RadCollapsiblePanel and change the back color or border of the container via the Edit UI elements dialog. 2. Save the changes and run the project. You will notice that the style is reset and the changes are not preserved. Workaround: Customize the style at runtime. The following help article gives you information about the internal elements structure of the RadCollapsiblePanel: https://docs.telerik.com/devtools/winforms/panels-and-labels/collapsiblepanel/structure