You're looking for the -webkit-transition property for webkit. That allows you to specify two separate CSS rules (for instance, two classes) and then the type of transition to be applied when switching those rules.
In this case, you could simply define the start and end heights (I did both height and width in the example below) as well as defining -webkit-transition-property for the properties you want transitioned, and -webkit-transition-duration for the duration:
div {
height: 200px;
width: 200px;
-webkit-transition-property: height, width;
-webkit-transition-duration: 1s;
background: red;
}
div:hover {
width: 500px;
height: 500px;
-webkit-transition-property: height, width;
-webkit-transition-duration: 1s;
background: red;
}
Tested in Safari. The Safari team also posted a pretty good write-up on CSS Visual Effects.
However, I would also recommend having another look at jQuery, as the newer CSS3 stuff won't be fully compatible with versions of IE.