customizing search button in theme

Hi, I am taking the twentyten theme and making my own customizations to it. One thing I am trying to do is change the current submit button. I was able to successfully do this in the CSS file, but the word ‘search’ sill appears over top of it and I want to take that out. Which file contains form code. I looked in search.php, but that only references the form code here it looks like.

<?php get_search_form(); ?>