Can anyone tell me what is the best book for CSS? So that i can design a website perfectly?
There are lots of good books on CSS. I recommend you search Amazon for CSS books and read the reviews. Not everyone likes the same approach, and I find the reviews really helpful in determining if a book is right for me or not.
No book will ensure you design a site perfectly, though. That’s up to you. 
Also do a search in the CSS forum on “CSS books” and you will find loads of similar questions with enough answers to keep you busy.
In my opinion the best one was this but its out of date now (not to mention out of print). (and not to mention I wrote half of it). You can still learn a lot from the [URL=“http://reference.sitepoint.com/css”]online reference even though it is out of date it does describe the fundamentals perfectly. It’s more of a manual than a how to though.
As Ralph said no book will teach you to design a website perfectly as that is down to you in the end. Learn as much as you can from many sources and then with practice and experience you will get better.