The CSS 3 transition specification makes it possible to make very impressive animations with just a few lines of CSS. Here´s a quick example for your reference. Vendor prefixes are still very necessary at the time of writing but will probably be less important soon.
a{ font-size:11px; background:white; color:black; -webkit-transition: 2s ease-in-out all; -moz-transition: 2s ease-in-out all; -ms-transition: 2s ease-in-out all; -o-transition: 2s ease-in-out all; transition: 2s ease-in-out all; } a:hover{ color:white; background:black; font-size:24px; }