Closed Issue: CollapsiblePanel should be more consistent with the Accordion Control - support header panel styling for collapsed and expanded states [12101]

In the Accordion control, you can control the image displayed when the current AccordionPane is open or not by using header and headerselected css classes. The Collapsible Panel, on the other hand, doesn't have a CollapsedCssClass or ExpandedCssClass to control the look of the header panel during these states. If a style can be applied based on whether the panel is expanded or collapsed, you won't need an image button as this can be provided through css class.

I have submitted a patch through the patch tool based on this requirement, which we are already using in a production site.
Comments: We will check it while working on future releases. Thank you for your comments!