public void DrawBackground(IDeviceContext graphics, int partId, int stateId, Rectangle bounds, Rectangle clipRect)
{
var b = new RECT(bounds);
var o = new DrawThemeBackgroundOptions(clipRect); // {OmitBorder = true, OmitContent = true};
using (var hdc = new Gdi32.SafeDCHandle(graphics))
DrawThemeBackgroundEx(hTheme, hdc, partId, stateId, ref b, o);
}
public static extern int DrawThemeBackgroundEx(SafeThemeHandle hTheme, SafeDCHandle hdc, int iPartId, int iStateId, ref RECT pRect, DrawThemeBackgroundOptions opts);