How to apply style using css in my email format

HI....
  i am sending a mail ( like:- if user creat an account then we are sending a welcome message to him). I apply style using css class. but problem is this...my mail is forwording successfully but its design is not perfect. my css is not applying.
 i m using css using .

how can i apply css to make my email formated


My email body is generated like following..:-
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