The major different between CSS and CSS3. The site which uses css3 loads faster then the site using css. The reason behind it is that css3 have new tags of codes added for example in previous version of css. If we need a rounded corner box, we had to create in photoshop and then use png format file on the website. But in css3 you need not worry about it. Using simple css3 tags you can created rounded box. You can perform as many effect using css3.
As well as the most good thing is you can use webkit keyframes for animation in css3. So you need not worry about using flash animation. Because you easily create good animation using css3.
Some of the basic css3 animation properties are as below.
@keyframes
animation-direction
animation-timing-function
Thanks