You should be able to target your H1 contentheading tag in CSS like so:
.contentheading h1 {
your style here;
}
BTW, I recently discovered a version of Joomla that has been changed/hacked for accessibility. It's called a8e Joomla and you can get it here;
www.a8ejoomla.com/
It's got all the tables removed and replaced with proper CSS styles and has h1 tags for titles etc...