Why css3 is invented?

Question

There is a css invented why we need css3?

Answer 1

Css3 is just the version specific of the generic Css language.
As all versionning system, higher version number means more recent, so mainly more improved and new features ^^

We need Css3 because it's more useful than previous version, and it will be consider as the most up to date version :P
But you're not forced to use specifities of Css3, and limit to specification of Css2 or even Css1, as each version are globaly backwards compatible...

Answer 2

It is for development purposes.
CSS3 is the latest evolution of the Cascading Style Sheets language and aims at extending CSS2.1. It brings a lot of long-awaited novelties, like rounded corners, shadows, gradients, transitions or animations, as well as new layouts like multi-columns, flexible box or grid layouts.