Thank you for your reply.
Yes, I understand the CSS margin and that it will be 45px. My question was how you knew that 45px would do the trick? I don't have my sub menu set to a set width of 90px. If that were the case, I would have seen that my 3rd level menu was starting in the middle and I would have guessed that 45px might have worked.
How did you arrive at the 45px number? Is this "magic" number to use for the left margin with setting the first sub level to auto width?