A few things....

First, and most important, you really really want to find out how to use firefox's web developer tools. Or chrome's version of the same thing. Don't use one of these browsers? Well you should.

These tools will allow you to highlight a element ( for instance the button) on the screen and it will tell you the structure of the page around it. WHich will let you immediately know which classess and IDs you can use.

This is much much faster than working it out by looking at the code.

Next you need to learn a little bit of css.

Code:
#createAcctSuccess .buttonRow forward,{
margin: 3px 0;
}
t

Without getting too far into a whole css tutorial this is wrong ( not sure how it works if it does)

It probably should read

Code:
#createAcctSuccess .buttonRow{
margin: 3px 0;
}
This targets all the elements with class 'buttonRow' that are inside elements with ID 'createAcctSuccess'.