Function lv_msgbox_add_header_button 

pub unsafe extern "C" fn lv_msgbox_add_header_button(
    obj: *mut lv_obj_t,
    icon: *const c_void,
) -> *mut lv_obj_t

Add a button to the header of to the message box. It also creates a header. @param obj pointer to a message box @param icon the icon of the button @return the created button