Hi Erhan,
I will add an extra CSS class on that button for the next release to make it easier.
For now I think you could style it with a selector like this:
.formwizard input[type="submit"] { }
though if it is already styled by the jqueryui button style classes you could style it with a selector like this:
.formwizard input.jqbutton { }
Hope that helps,
Joe