There are many ways to style input buttons in CSS. And this is how I do it.

HTML

<input type="submit" name="submit" value="Send" id="submit" />

CSS

#submit {
 color: #fff;
 font-size: 0;
 width: 135px;
 height: 60px;
 border: none;
 margin: 0;
 padding: 0;
 background: #0c0 url(images/send-now.gif) 0 0 no-repeat; 
}

And that's it, you will have a nice fancy button like below:

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