If you are a xenforo newcomer and want to mess with the style properties you often don't know what a property is referring to (e.g. @popupControlClosedHover etc.). Some properties have tooltips with small explanations, some don't. From my own experience I can tell that it's very convenient and user-friendly to have tooltips with sample pictures embedded. This way you know immediately what a style property is referring to and can save yourself the hassle of trial and error.