9591308a__info___Pseudo_class_selectors_CSS_Pseudo_class_selectors_Purpose
[Pseudo-class selector] :hover [Purpose] 
Controls the appearance of an element while it is being hovered over with a mouse or other pointing device. While it is heavily associated with the a tag, CSS does not explicitly specify this association. In modern browsers, :hover can be applied to any arbitrary element, such as img:hover.
demosthenes.info – Pseudo-class selectors
Purpose