I would like to suggest a panel setting that allows you to change the corner radius of the panel, regardless of the theme. I always just use breeze, but I really want more rounded corners on the panel, but there doesn’t seem to be a way to do that without changing the plasma style, which I don’t want to do.
As I understand it, right now the corner radius of the panel is completely controlled by an SVG file in the theme, but I think it would be a lot more convenient and make KDE more customizable if there’s just a setting along with the other panel settings, that allows you to control the panel corner radius using a slider or a pixel/percentage value.