Hide Toggle Advanced link via CSS

Hi your plugin is one the best I have tried far invoicing . Thus I am using for a project and most likely the add ons.

My client would like to hide the Toggle Advanced link so as not to be played around and will not confuse newbie users.

I did try CSS below via Chrome browser which seems to be ok but not if I place in Simple CSS entry field.

span#wpi_button_show_advanced {
display: none;
}

Hope for your assistance on how to hide the Toggle Advanced link

https://ww.wp.xz.cn/plugins/wp-invoice/